Control system and method thereof for multispeed transmission

ABSTRACT

An electro-hydraulic control system for a multispeed transmission having a plurality of torque-transmitting mechanisms includes a controller for operably controlling the transmission, a fluid source for supplying hydraulic fluid, and a plurality of torque-transmitting mechanisms being operably selected between an applied and an unapplied state to achieve a plurality of ranges including at least one reverse, a neutral, and a plurality of forward ranges. The system includes a plurality of trim systems having pressure control solenoids and trim valves. The system may also include one or more shift valves disposed in fluid communication with the fluid source and being capable of moving between stroked and de-stroked positions. In any given range, only two of the plurality of torque-transmitting mechanisms may be applied. Moreover, three of the plurality of pressure control solenoids are normally high solenoids, and the remaining solenoids are normally low solenoids.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/527,202, filed Jun. 30, 2017, the disclosure ofwhich is hereby incorporated by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to a method of controlling a transmissionsystem, and in particular to a method of controlling hydraulic fluid fora multispeed transmission.

BACKGROUND

Multiple speed transmission uses a number of friction clutches orbrakes, planetary gearsets, shafts, and other elements to achieve aplurality of gear or speed ratios. The transmission architecture, i.e.,the packaging or layout of the aforementioned elements, is determinedbased on cost, size, packaging constraints, and desired ratios. Acontrol system is needed for controlling these elements and providedesirable shift quality. Moreover, with more ranges being provided forimproved fuel economy among other reasons, the control system mustensure the correct clutches or brakes are applied in any given range,and further provide for fault ranges in the event of a loss ofelectrical power. With more forward and reverse ranges for any givenmultispeed transmission, the control system continues to increase incomplexity.

SUMMARY

In one embodiment of the present disclosure, an electro-hydrauliccontrol system for a multispeed transmission includes a controller foroperably controlling the transmission; a fluid source for supplyinghydraulic fluid; a plurality of torque-transmitting mechanisms beingoperably selected between an applied and an unapplied state to achieve aplurality of ranges including at least one reverse, a neutral, and aplurality of forward ranges, wherein in any one of the plurality offorward ranges only two of the plurality of torque-transmittingmechanisms are in the applied state; a plurality of trim systems beingin electrical communication with the controller and in fluidcommunication with the fluid source, wherein each of the plurality oftrim systems includes a pressure control solenoid and a trim valve; aplurality of shift valves each of which is disposed in fluidcommunication with the fluid source and configured to move between astroked position and a de-stroked position, the plurality of shiftvalves including at least a first shift valve, a second shift valve anda third shift valve; wherein, a latch is formed by hydraulic fluid inthe system against at least one of the first, second and third shiftvalves during a shift from one of the plurality of forward ranges toneutral such that the at least one of the first, second and third shiftvalves is maintained in its stroked position due to the latch.

In a first example of this embodiment, the latch is formed by a checkvalve located between the at least one of the first, second and thirdshift valves and an exhaust passage. In a second example, at least oneof the first, second and third shift valves is fluidly biased to movefrom its stroked position to its de-stroked position during the shift toneutral. In a third example, three of the first, second, third, fourthand fifth pressure control solenoids comprise normally high solenoids,and the other two solenoids comprise normally low solenoids. In a fourthexample, a pressure switch may be disposed in fluid communication withthe at least one of the first, second and third shift valves and inelectrical communication with the controller, the pressure switchconfigured to detect a position of the at least one of the first, secondand third shift valves.

In a fifth example, a first torque-transmitting mechanism and a secondtorque-transmitting mechanism are in their applied states in a firstrange of the plurality of forward ranges; and the firsttorque-transmitting mechanism remains in its applied state and thesecond torque-transmitting mechanism exhausts to its unapplied stateduring the shift to neutral. In a sixth example, the latch is formed bya flow restriction and check valve located between the at least one ofthe first, second and third shift valves and an exhaust passage.

In another embodiment of the present disclosure, an electro-hydrauliccontrol system for a multispeed transmission includes a controller foroperably controlling the transmission; a fluid source for supplyinghydraulic fluid; a plurality of torque-transmitting mechanisms beingoperably selected between an applied and an unapplied state to achieve aplurality of ranges including at least one reverse, a neutral, and aplurality of forward ranges, wherein in any one of the plurality offorward ranges only two of the plurality of torque-transmittingmechanisms are in the applied state; a plurality of trim systems beingin electrical communication with the controller and in fluidcommunication with the fluid source, wherein each of the plurality oftrim systems includes a pressure control solenoid and a trim valve; aplurality of shift valves each of which is disposed in fluidcommunication with the fluid source and configured to move between astroked position and a de-stroked position, the plurality of shiftvalves including at least a first shift valve, a second shift valve anda third shift valve; a first shift solenoid and a second shift solenoideach of which is disposed in electrical communication with thecontroller, the first shift solenoid being operably controlled betweenan energized and de-energized states to control movement of the firstand second shift valves, and the second shift solenoid being operablycontrolled between an energized and de-energized states to controlmovement of the third shift valve; wherein in a first forward range ofthe plurality of forward ranges, a first torque-transmitting mechanismand a second torque-transmitting mechanism are in their applied states;the first shift solenoid is energized to control movement of the firstand second shift valves to their stroked positions such that hydraulicfluid at a head of each of the first and second shift valves forces bothshift valves to their stroked positions; further wherein, when shiftingfrom the first forward range to neutral, the first torque-transmittingmechanism remains in its applied state as the only appliedtorque-transmitting mechanism, and the second torque-transmittingmechanism is exhausted.

In one example of this embodiment, a latch is formed by hydraulic fluidin the system against at least one of the first, second and third shiftvalves when shifting to neutral from the first forward range. In asecond example, at least one of the first and second shift valves ismaintained in its stroked position due to the latch. In a third example,the first and second shift valves are maintained in their strokedpositions due to the latch. In another example, the latch is formed by acheck valve located between the at least one of the first, second andthird shift valves and an exhaust passage. In a further example, thelatch is formed by a flow restriction and check valve located betweenthe at least one of the first, second and third shift valves and anexhaust passage. In yet another example, a pressure switch may bedisposed in fluid communication with the at least one of the first,second and third shift valves and in electrical communication with thecontroller, the pressure switch configured to detect a position of theat least one of the first, second and third shift valves.

In a further embodiment of the present disclosure, an electro-hydrauliccontrol system for a multispeed transmission includes a controller foroperably controlling the transmission; a fluid source for supplyinghydraulic fluid; a plurality of torque-transmitting mechanisms beingoperably selected between an applied and an unapplied state to achieve aplurality of ranges including at least one reverse, a neutral, and aplurality of forward ranges, wherein in any one of the plurality offorward ranges only two of the plurality of torque-transmittingmechanisms are in the applied state; a plurality of trim systems beingin electrical communication with the controller and in fluidcommunication with the fluid source, wherein each of the plurality oftrim systems includes a pressure control solenoid and a trim valve; aplurality of shift valves each of which is disposed in fluidcommunication with the fluid source and configured to move between astroked position and a de-stroked position, the plurality of shiftvalves including at least a first shift valve, a second shift valve anda third shift valve; a first shift solenoid disposed in electricalcommunication with the controller, the first shift solenoid beingoperably controlled between an energized and de-energized states tocontrol movement of the first and second shift valves; and a secondshift solenoid disposed in electrical communication with the controller,the second shift solenoid being operably controlled between an energizedand de-energized states to control movement of the third shift valve;wherein, movement of the first shift valve between its stroked andde-stroked positions is operably controlled by the controller to selecta desired range of the plurality of ranges.

In one example of this embodiment, in neutral and the at least onereverse, the controller operably controls movement of the first shiftvalve to its de-stroked position; and in each of the plurality offorward ranges, the controller operably controls movement of the firstshift valve to its stroked position. In another example, a plurality ofpressure switches is disposed in electrical communication with thecontroller, the plurality of pressure switches includes at least a firstpressure switch, a second pressure switch and a third pressure switch.In yet another example, the first pressure switch is in fluidcommunication with the first shift valve to detect a position thereof;the second pressure switch is in fluid communication with the secondshift valve to detect a position thereof; and the third pressure switchis in fluid communication with the third shift valve to detect aposition thereof.

In a further example, in neutral and the at least one reverse, thecontroller operably controls movement of the first shift valve to itsde-stroked position; in each of the plurality of forward ranges, thecontroller operably controls movement of the first shift valve to itsstroked position; the first pressure switch is either pressurized or notpressurized based on the position of the first shift valve; and thecontroller operably detects the position of the first shift valve basedon whether the first pressure switch is pressurized or not pressurized.

In yet a further example of this embodiment, the system may include afourth pressure switch disposed in fluid communication with a first trimsystem of the plurality of trim systems; and a first torque-transmittingmechanism of the plurality of torque-transmitting mechanisms being influid communication with the first trim system; wherein, the fourthpressure switch is either pressurized or not pressurized based upon aposition of the trim valve of the first trim system; further wherein,the position of the trim valve and whether the first torque-transmittingmechanism is in its applied state or unapplied state is operablydetectable by the controller based on if the fourth pressure switch ispressurized or not.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned aspects of the present disclosure and the manner ofobtaining them will become more apparent and the disclosure itself willbe better understood by reference to the following description of theembodiments of the disclosure, taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a block diagram and schematic view of one illustrativeembodiment of a powered vehicular system;

FIG. 2 is a partial controls schematic of a multispeed transmissionsystem;

FIG. 3 is a hydraulic control schematic of the system of FIG. 2 inreverse;

FIG. 4 is a hydraulic control schematic of the system of FIG. 2 inneutral or park;

FIG. 5 is one embodiment of a hydraulic control schematic of the systemof FIG. 2 in a first range;

FIG. 6 is another embodiment of a hydraulic control schematic of thesystem of FIG. 2 in first range;

FIG. 7 is a hydraulic control schematic of the system of FIG. 2 insecond range;

FIG. 8 is a hydraulic control schematic of the system of FIG. 2 in thirdrange;

FIG. 9 is a hydraulic control schematic of the system of FIG. 2 infourth range;

FIG. 10 is a hydraulic control schematic of the system of FIG. 2 infifth range;

FIG. 11 is a hydraulic control schematic of the system of FIG. 2 insixth range;

FIG. 12 is a hydraulic control schematic of the system of FIG. 2 inseventh range;

FIG. 13 is a hydraulic control schematic of the system of FIG. 2 ineighth range;

FIG. 14 is a hydraulic control schematic of the system of FIG. 2 inninth range;

FIG. 15 is a hydraulic control schematic of the system of FIG. 2 in afirst power-off range;

FIG. 16 is a hydraulic control schematic of the system of FIG. 2 in asecond power-off range;

FIG. 17 is a hydraulic control schematic of the system of FIG. 2 in athird power-off range;

FIG. 18 is one embodiment of a schematic of a first shift valve;

FIG. 19 is one embodiment of a schematic of a second shift valve;

FIG. 20 is one embodiment of a schematic of a third shift valve;

FIG. 21 is one embodiment of a mechanization table of the multispeedtransmission system of FIG. 2;

FIG. 22 is one embodiment of a shift availability table of themultispeed transmission system of FIG. 2; and

FIG. 23 is a legend of the different fluid circuits or paths in thehydraulic control schematics of FIGS. 3-17.

Corresponding reference numerals are used to indicate correspondingparts throughout the several views.

DETAILED DESCRIPTION

The embodiments of the present disclosure described below are notintended to be exhaustive or to limit the disclosure to the preciseforms disclosed in the following detailed description. Rather, theembodiments are chosen and described so that others skilled in the artmay appreciate and understand the principles and practices of thepresent disclosure.

The terminology used herein is for the purpose of describing particularillustrative embodiments only and is not intended to be limiting. Asused herein, the singular forms “a”, “an” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. Similarly, plural forms may have been used to describeparticular illustrative embodiments when singular forms would beapplicable as well. The terms “comprises,” “comprising,” “including,”and “having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

Referring now to FIG. 1, a block diagram and schematic view of oneillustrative embodiment of a vehicular system 100 having a drive unit102 and transmission 118 is shown. In the illustrated embodiment, thedrive unit 102 may include an internal combustion engine, diesel engine,electric motor, or other power-generating device. The drive unit 102 isconfigured to rotatably drive an output shaft 104 that is coupled to aninput or pump shaft 106 of a conventional torque converter 108. Theinput or pump shaft 106 is coupled to an impeller or pump 110 that isrotatably driven by the output shaft 104 of the drive unit 102. Thetorque converter 108 further includes a turbine 112 that is coupled to aturbine shaft 114, and the turbine shaft 114 is coupled to, or integralwith, a rotatable input shaft 124 of the transmission 118. Thetransmission 118 can also include an internal pump 120 for buildingpressure within different flow circuits (e.g., main circuit, lubecircuit, etc.) of the transmission 118. The pump 120 can be driven by ashaft 116 that is coupled to the output shaft 104 of the drive unit 102.In this arrangement, the drive unit 102 can deliver torque to the shaft116 for driving the pump 120 and building pressure within the differentcircuits of the transmission 118.

The transmission 118 can include a planetary gear system 122 having anumber of automatically selected gears. An output shaft 126 of thetransmission 118 is coupled to or integral with, and rotatably drives, apropeller shaft 128 that is coupled to a conventional universal joint130. The universal joint 130 is coupled to, and rotatably drives, anaxle 132 having wheels 134A and 134B mounted thereto at each end. Theoutput shaft 126 of the transmission 118 drives the wheels 134A and 134Bin a conventional manner via the propeller shaft 128, universal joint130 and axle 132.

A conventional lockup clutch 136 is connected between the pump 110 andthe turbine 112 of the torque converter 108. The operation of the torqueconverter 108 is conventional in that the torque converter 108 isoperable in a so-called “torque converter” mode during certain operatingconditions such as vehicle launch, low speed and certain gear shiftingconditions. In the torque converter mode, the lockup clutch 136 isdisengaged and the pump 110 rotates at the rotational speed of the driveunit output shaft 104 while the turbine 112 is rotatably actuated by thepump 110 through a fluid (not shown) interposed between the pump 110 andthe turbine 112. In this operational mode, torque multiplication occursthrough the fluid coupling such that the turbine shaft 114 is exposed todrive more torque than is being supplied by the drive unit 102, as isknown in the art. The torque converter 108 is alternatively operable ina so-called “lockup” mode during other operating conditions, such aswhen torque multiplication is not needed. In the lockup mode, the lockupclutch 136 is engaged and the pump 110 is thereby secured directly tothe turbine 112 so that the drive unit output shaft 104 is directlycoupled to the input shaft 124 of the transmission 118, as is also knownin the art.

The transmission 118 further includes an electro-hydraulic system 138that is fluidly coupled to the planetary gear system 122 via a number,J, of fluid paths, 140 ₁-140 _(J), where J may be any positive integer.The electro-hydraulic system 138 is responsive to control signals toselectively cause fluid to flow through one or more of the fluid paths,140 ₁-140 _(J), to thereby control operation, i.e., engagement anddisengagement, of a plurality of corresponding friction devices in theplanetary gear system 122. The plurality of friction devices mayinclude, but are not limited to, one or more conventional brake devices,one or more torque transmitting devices, and the like. Generally, theoperation, i.e., engagement and disengagement, of the plurality offriction devices is controlled by selectively controlling the frictionapplied by each of the plurality of friction devices, such as bycontrolling fluid pressure to each of the friction devices. In oneexample embodiment, which is not intended to be limiting in any way, theplurality of friction devices include a plurality of brake and torquetransmitting devices in the form of conventional clutches that may eachbe controllably engaged and disengaged via fluid pressure supplied bythe electro-hydraulic system 138. In any case, changing or shiftingbetween the various gears of the transmission 118 is accomplished in aconventional manner by selectively controlling the plurality of frictiondevices via control of fluid pressure within the number of fluid paths140 ₁-140 _(J).

The system 100 further includes a transmission control circuit 142 thatcan include a memory unit 144. The transmission control circuit 142 isillustratively microprocessor-based, and the memory unit 144 generallyincludes instructions stored therein that are executable by a processorof the transmission control circuit 142 to control operation of thetorque converter 108 and operation of the transmission 118, i.e.,shifting between the various gears of the planetary gear system 122. Itwill be understood, however, that this disclosure contemplates otherembodiments in which the transmission control circuit 142 is notmicroprocessor-based, but is configured to control operation of thetorque converter 108 and/or transmission 118 based on one or more setsof hardwired instructions and/or software instructions stored in thememory unit 144.

In the system 100 illustrated in FIG. 1, the torque converter 108 andthe transmission 118 include a number of sensors configured to producesensor signals that are indicative of one or more operating states ofthe torque converter 108 and transmission 118, respectively. Forexample, the torque converter 108 illustratively includes a conventionalspeed sensor 146 that is positioned and configured to produce a speedsignal corresponding to the rotational speed of the pump shaft 106,which is the same rotational speed of the output shaft 104 of the driveunit 102. The speed sensor 146 is electrically connected to a pump speedinput, PS, of the transmission control circuit 142 via a signal path152, and the transmission control circuit 142 is operable to process thespeed signal produced by the speed sensor 146 in a conventional mannerto determine the rotational speed of the pump shaft 106/drive unitoutput shaft 104.

The transmission 118 illustratively includes another conventional speedsensor 148 that is positioned and configured to produce a speed signalcorresponding to the rotational speed of the transmission input shaft124, which is the same rotational speed as the turbine shaft 114. Theinput shaft 124 of the transmission 118 is directly coupled to, orintegral with, the turbine shaft 114, and the speed sensor 148 mayalternatively be positioned and configured to produce a speed signalcorresponding to the rotational speed of the turbine shaft 114. In anycase, the speed sensor 148 is electrically connected to a transmissioninput shaft speed input, TIS, of the transmission control circuit 142via a signal path 154, and the transmission control circuit 142 isoperable to process the speed signal produced by the speed sensor 148 ina conventional manner to determine the rotational speed of the turbineshaft 114/transmission input shaft 124.

The transmission 118 further includes yet another speed sensor 150 thatis positioned and configured to produce a speed signal corresponding tothe rotational speed of the output shaft 126 of the transmission 118.The speed sensor 150 may be conventional, and is electrically connectedto a transmission output shaft speed input, TOS, of the transmissioncontrol circuit 142 via a signal path 156. The transmission controlcircuit 142 is configured to process the speed signal produced by thespeed sensor 150 in a conventional manner to determine the rotationalspeed of the transmission output shaft 126.

In the illustrated embodiment, the transmission 118 further includes oneor more actuators configured to control various operations within thetransmission 118. For example, the electro-hydraulic system 138described herein illustratively includes a number of actuators, e.g.,conventional solenoids or other conventional actuators, that areelectrically connected to a number, J, of control outputs, CP₁-CP_(J),of the transmission control circuit 142 via a corresponding number ofsignal paths 72 ₁-72 _(J) where J may be any positive integer asdescribed above. The actuators within the electro-hydraulic system 138are each responsive to a corresponding one of the control signals,CP₁-CP_(J), produced by the transmission control circuit 142 on one ofthe corresponding signal paths 72 ₁-72 _(J) to control the frictionapplied by each of the plurality of friction devices by controlling thepressure of fluid within one or more corresponding fluid passageway 140₁-140 _(J), and thus control the operation, i.e., engaging anddisengaging, of one or more corresponding friction devices, based oninformation provided by the various speed sensors 146, 148, and/or 150.

The friction devices of the planetary gear system 122 are illustrativelycontrolled by hydraulic fluid which is distributed by theelectro-hydraulic system in a conventional manner. For example, theelectro-hydraulic system 138 illustratively includes a conventionalhydraulic positive displacement pump 120 which distributes fluid to theone or more friction devices via control of the one or more actuatorswithin the electro-hydraulic system 138. In this embodiment, the controlsignals, CP₁-CP_(J), are illustratively analog friction device pressurecommands to which the one or more actuators are responsive to controlthe hydraulic pressure to the one or more frictions devices. It will beunderstood, however, that the friction applied by each of the pluralityof friction devices may alternatively be controlled in accordance withother conventional friction device control structures and techniques,and such other conventional friction device control structures andtechniques are contemplated by this disclosure. In any case, however,the analog operation of each of the friction devices is controlled bythe control circuit 142 in accordance with instructions stored in thememory unit 144.

In the illustrated embodiment, the system 100 further includes a driveunit control circuit 160 having an input/output port (I/O) that iselectrically coupled to the drive unit 102 via a number, K, of signalpaths 162, wherein K may be any positive integer. The drive unit controlcircuit 160 may be conventional, and is operable to control and managethe overall operation of the drive unit 102. The drive unit controlcircuit 160 further includes a communication port, COM, which iselectrically connected to a similar communication port, COM, of thetransmission control circuit 142 via a number, L, of signal paths 164,wherein L may be any positive integer. The one or more signal paths 164are typically referred to collectively as a data link. Generally, thedrive unit control circuit 160 and the transmission control circuit 142are operable to share information via the one or more signal paths 164in a conventional manner. In one embodiment, for example, the drive unitcontrol circuit 160 and transmission control circuit 142 are operable toshare information via the one or more signal paths 164 in the form ofone or more messages in accordance with a Society of AutomotiveEngineers (SAE) J-1939 communications protocol, although this disclosurecontemplates other embodiments in which the drive unit control circuit160 and the transmission control circuit 142 are operable to shareinformation via the one or more signal paths 164 in accordance with oneor more other conventional communication protocols (e.g., from aconventional databus such as J1587 data bus, J1939 data bus, IESCAN databus, GMLAN, Mercedes PT-CAN).

Referring to FIG. 2, a hydraulic control system is illustrated for amultispeed transmission system 200. The system 200 may include similarfeatures of the transmission 118 of FIG. 1. For example, the system 200may include a torque converter 202 or other fluid-coupling device forfluidly coupling the transmission system 200 to an engine or other primemover 102. The torque converter 202 may include a lockup clutch (notshown) similar to the clutch 136 of FIG. 1. Moreover, the transmissionsystem 200 may include a main fluid pump 204 for providing hydraulicfluid and pressure throughout the system. The pump 204 may be similar tothe internal pump 120 of FIG. 1. Here, the pump 204 may be fluidlycoupled to a reservoir 206 or sump that provides a fluid to a suctionside of the pump 204. In this disclosure, the pump 204 may be referredto as the fluid or pressure source of the system 200.

The transmission system 200 may include other systems or sub-systemssuch as a pressure regulator system, a lube system, a converter system,and a cooler system. In FIG. 2, the transmission system 200 may includea main regulator 208 that is in fluid communication with the pump 204.The main regulator 208 may be a valve or other fluid-regulatingmechanism for regulating a main pressure in the system 200. In thisdisclosure, a full main pressure may be provided by the pump 204 to thetransmission system 200. The main regulator 208 may regulate thispressure, and as will be described below, other solenoids and the likemay be triggered to further regulate main pressure. In any event, themain regulator forms part of the pressure regulator system, and mainpressure flows from the main regulator 208 to a main pressure circuit218 of the transmission system 200 as will be described below.

The main regulator 208 is further fluidly coupled to the convertersystem. The converter system may include the torque converter 202, aconverter relief 210, and a converter flow 214. In one example, theconverter relief 210 and converter flow 214 may be valves. Hydraulicfluid may flow from the main regulator 208 to the converter relief 210and converter flow 214. Moreover, fluid may flow from the converter flow214 to the torque converter 202 via a converter-in passage 222, andfluid may flow from the torque converter 202 to the converter flow 214via a converter-out passage 220. In this way, fluid pressure can flow toand from the torque converter to better regulate a fluid operatingtemperature in the torque converter 202 and provide cooler fluid toprotect the lockup clutch, if applicable. There may be other reasons oradvantages for fluidly coupling the torque converter 202 to theconverter flow 214 as may be appreciated by the skilled artisan.

The transmission system 200 may also include a lube system and a coolersystem. The lube system may include a lube regulator 212 for regulatingpressure to cool clutches, brakes and the like in the system 200. Thecooler system may include a cooler 216, such as a vehicle cooler, thatmay be disposed outside of the transmission system 200. Nevertheless,the cooler 216 may be in fluid communication with the converter flow 214and the lube regulator 212, as shown in FIG. 2. The cooler 216 mayfurther be configured to provide cooler flow 224 to the lube circuit.

FIG. 2 is only one embodiment of a transmission system. There may beother components or systems that form part of embodiments different fromthe one shown in FIG. 2. The teachings of this disclosure is notintended to be limited to any particular embodiment.

The present disclosure provides an electro-hydraulic control system forcontrolling a multispeed transmission. The multispeed transmission mayinclude a plurality of forward and reverse speed ratios. Moreover, themultispeed transmission may include an input, an output, a plurality ofplanetary gearsets, and a plurality of torque-transmitting mechanismswhich are selectively engageable to achieve the plurality of forward andreverse speed ratios. In one example, the multispeed transmission may bea nine-speed transmission with an input, an output, a first planetarygearset, a second planetary gearset, and third planetary gearset, and afourth planetary gearset. Each planetary gearset may be disposed betweenthe input and the output, and each planetary gearset may include a sungear, a ring gear, and a carrier member. Further, in this example, thetransmission may include a plurality of interconnecting members forcoupling the planetary gearsets and the torque-transmitting mechanismsto one another and the input and output. One non-limiting example of amultispeed transmission architecture that may be controlled by theteachings of this disclosure is disclosed in U.S. Pat. No. 7,364,527,issued on Apr. 29, 2008 and assigned to General Motors Corporation, thedisclosure of which is hereby incorporated by reference.

Referring to FIGS. 3-17, an electro-hydraulic control system 300 isshown for a multispeed transmission in a plurality of ranges includingat least one neutral and one reverse range. The electro-hydrauliccontrol system 300 may be similarly situated as the electro-hydraulicsystem 138 of FIG. 1. In particular, the electro-hydraulic controlsystem 300 may be in electrical communication with a controller such asa transmission control circuit 142 illustrated in FIG. 1. Moreover, theelectro-hydraulic control system 300 may include a plurality of fluidpaths (e.g., fluid paths 140 ₁-140 _(j)) for fluidly coupling to aplanetary gear system 122 such as the one shown in FIG. 1. In otherembodiments, the control system 300 may be electrically or fluidlycoupled to other systems or subsystems of a multispeed transmissionsystem.

The electro-hydraulic control system 300 may include a plurality ofvalves and solenoids for controlling the selective engagement of one ormore clutches or brakes. Each clutch or brake may be referred to as atorque-transmitting mechanism for purposes of this disclosure. Inaddition, and as will be described below, the system 300 may includepressure switches for detecting pressure within a certain circuit orfluid path in the system 300. Other mechanisms will be described in thisdisclosure. It is worth noting that FIGS. 3-17 illustrate only oneembodiment of an electro-hydraulic control system for a multispeedtransmission. This disclosure, however, is not intended to be limited toonly this embodiment.

Turning specifically to FIG. 3, the electro-hydraulic control system 300may be in fluid communication with the transmission system 200 of FIG.2. In particular, a fluid source 302 to the control system 300 may befluidly coupled to the pump 204 via the main regulator 208 and the mainpressure circuit 218. Hydraulic fluid may be supplied from the pump 204to the control system 300 and regulated by the main regulator 208. Assuch, fluid from the pressure source 302 may be referred to as mainpressure. The various fluid pressures and fluid lines in theelectro-hydraulic control system 300 are identified in a legend shown inFIG. 23 of this disclosure. These fluid pressures include main pressure,control main pressure, exhaust backfill pressure, exhaust pressure, mainmodulated pressure, torque converter lockup clutch signal pressure,torque converter lockup clutch pressure, pressure control solenoidsignal pressures, and clutch pressures. In other embodiments, there maybe additional or fewer signal pressures or fluid pressures in a controlsystem, and the illustrative embodiments of the present disclosure arenot intended to be limiting in this manner.

Referring to FIG. 3, the electro-hydraulic control system 300 mayinclude a plurality of trim systems, with each trim system including asolenoid and a trim valve. For example, a first trim system may includea torque converter clutch trim solenoid 304 (i.e., TCC solenoid) and atorque converter clutch trim valve 306. Also shown adjacent to the TCCtrim solenoid 304 but not labeled is an accumulator (to the left of thesolenoid 304 in FIG. 3). Activation of the TCC trim system may providehydraulic fluid through a TCC flow path to the converter flow 214. Thefluid may flow from the converter flow 214 to apply the lockup clutch ofthe torque converter 202 via the converter in flow path 222. This isbest shown in FIGS. 2 and 6.

Each of the trim systems depicted in FIGS. 3-17 include an accumulator,although in other embodiments there may not be an accumulator for eachtrim system. The accumulator is a small valve that strokes according toan output pressure of the solenoid. When it strokes or de-strokes, thereis a volume of fluid that comes from the solenoid output or flows backthrough the solenoid. The accumulator may be any conventional mechanismfor providing a more stable controls system.

A second trim system includes a first pressure control solenoid 308 anda first pressure control trim valve 310. The trim system may include anaccumulator as shown in FIG. 3. The first pressure control solenoid 308may be referred to as a normally-high pressure control solenoid. Forpurposes of this disclosure, a normally-high pressure control solenoidoutputs full pressure when there is no current being supplied to thesolenoid. In other words, if electrical power is lost or disconnected tothe first pressure control solenoid 308, its default position is tooutput full pressure to stroke the first pressure control trim valve310.

As also shown, hydraulic fluid may flow through the second trim systemto apply a first torque-transmitting mechanism, C1. C1 may be either aclutch or a brake. In FIG. 3, C1 is unapplied and hydraulic fluid isexhausted to backfill as shown. Exhaust backfill and exhaust may simplyrefer to hydraulic fluid being released or returned to the reservoir206.

Another trim system in FIG. 3 includes a second pressure controlsolenoid 312 and a second pressure control trim valve 314. Similar tothe first pressure control solenoid 308, the second pressure controlsolenoid 312 may be a normally-high pressure control solenoid. Thus, ifelectrical power is lost or disconnected to the second pressure controlsolenoid 312, it defaults to full output pressure to stroke the secondpressure control trim valve 314.

A further trim system in the control system 300 includes a thirdpressure control solenoid 316 and a third pressure control trim valve318. Similar to the first and second trim solenoids, the third pressurecontrol solenoid 316 may be a normally-high pressure control solenoid.Thus, if electrical power is lost or disconnected to the third pressurecontrol solenoid 316, it defaults to full output pressure to stroke thethird pressure control trim valve 318. Moreover, when the third pressurecontrol trim valve 318 is stroked, hydraulic fluid is able to flow andapply a third torque-transmitting mechanism, C3. Similar to C1, C3 maybe a clutch or brake.

The electro-hydraulic control system 300 further includes a trim systemformed by a fourth pressure control solenoid 320 and a fourth pressurecontrol trim valve 322. The fourth pressure control solenoid 320 may bea normally-low pressure control solenoid. Thus, unlike the normally-highpressure control solenoids, the normally-low pressure control solenoidsproduce zero output pressure when there is no current supplied to thesolenoid. If the fourth pressure control solenoid 320 is actuated orenergized by a transmission controller or control circuit, andelectrical power is lost, the fourth pressure control solenoid 320defaults to zero output pressure and the fourth pressure control trimvalve 322 de-strokes.

This trim system may also control fluid pressure to a fourthtorque-transmission mechanism, C4. C4 may be a clutch or a brake. Whenthe fourth pressure control trim valve 322, or simply the fourth trimvalve, moves to its stroked position, fluid pressure may fill and applyC4. However, when electrical power is lost, the fourth pressure controlsolenoid 320 de-energizes and the fourth trim valve 322 de-strokes thusblocking hydraulic fluid from applying C4. This will be furtherdescribed below.

Another trim system in the control system 300 includes a fifth pressurecontrol solenoid 324 and a fifth pressure control trim valve 326. Inthis embodiment, the fifth pressure control solenoid 324 is anothernormally-low pressure control solenoid that defaults to zero outputpressure when electrical current is no longer supplied to the solenoid.As such, the fifth pressure control trim valve 326, or simply fifth trimvalve 326, de-strokes when electrical power is lost.

As shown in FIG. 3, the fifth pressure control solenoid 324 and fifthtrim valve 326 may control hydraulic fluid to apply a sixthtorque-transmitting mechanism, C6. C6 may be a clutch or brake. When thefifth trim valve 326 is stroked, fluid may fill and apply C6. When thevalve is de-stroked, C6 may be unapplied. Another feature of this trimsystem in the inclusion of a boost plug 328. The boost plug 328 mayinclude a hollow opening or channel 344 defined therein for fluid topass through the plug 328 and move the fifth trim valve 326. As will bedescribed below, the boost plug 328 allows for a different gain to berealized by this trim system.

The control system 300 may further include a second torque-transmittingmechanism, C2, and a fifth torque-transmitting mechanism, C5. C2 and C5may be either a clutch or a brake. Hydraulic fluid for applying eitherC2 or C5 may flow through fluid passages defined by a relative positionof the second trim valve 314.

The electro-hydraulic control system 300 of FIG. 3 further illustrates apair of on-off shift solenoids 330, 332. Each solenoid may be energizedor de-energized by the controller, e.g., the transmission controller ortransmission control circuit 142. When the solenoid is energized, i.e.,it is considered “on”, the solenoid is capable of outputting a controlpressure. When the solenoid is de-energized, i.e., it is referred to asbeing “off,” the solenoid does not output any control pressure.

In this disclosure, control pressure is a pressure that is fed from themain pressure circuit 218 or pressure source 302 but it is regulated ata maximum pressure that is generally lower than main pressure. Moreover,control pressure, i.e., “control main pressure”, is referred to as afeed pressure to all actuators. The control pressure may be regulated,for example, at 110 psi. This is only one example as control pressuremay be regulated at a different pressure for other embodiments. Bycontrast, main pressure may exceed control pressure based on aparticular torque requirement of the transmission. For example, in oneembodiment, main pressure may vary between 50-250 psi, whereas controlpressure may be limited at a regulated pressure (e.g., 110 psi).

Control pressure may be used to control the solenoids in the controlsystem 300 so that the maximum output pressure of the solenoids iscontrol pressure. To achieve control pressure, main pressure is suppliedfrom the pressure source 302 into a control main valve 334. Hydraulicfluid flowing out of the control main valve 334 is the control pressure,which then flows through a control main filter 336 to remove any debrisor unwanted particulates in the fluid. Control pressure then flows toeach of the aforementioned pressure control solenoids and the on/offsolenoids. Control pressure may also be fed through the differentactuators or shift valves, which will be described below. Moreover,control pressure pressurizes pressure switches in the control system300.

Another mechanism for reducing or otherwise regulating main pressure isa main modulated solenoid 340. The main modulated solenoid 340 outputs areduced main pressure, and the solenoid may be energized andde-energized via the controller. Although not shown in FIG. 3, modulatedmain pressure from the main modulated solenoid 340 may flow to the mainregulator 208 in FIG. 2 to increase or decrease main pressure based onsolenoid output.

The control system 300 includes a plurality of different valvesincluding an exhaust backfill relief valve 338 and an exhaust backfillvalve 342. In each case, fluid that pressurizes either valve may beexhausted to the reservoir 206. Another type of valve in the controlsystem 300 is a check valve 352. In FIG. 3, there are several checkvalves 352 illustrated in various paths to restrict or prevent flow in acertain direction of the flow path. The check valve 352 may be anyconventional check valve for purposes of this disclosure.

The control system 300 further includes a plurality of shift valves oractuators. The shift valves may function differently from the trimvalves. The aforementioned trim valves, for example, may be used formodulating pressure to a desired clutch pressure. Here, main pressuremay be trimmed to a desirable clutch or trim pressure. On the otherhand, the shift valves transition or redirect hydraulic fluid from oneflow path to a different flow path.

In the illustrated embodiment of FIGS. 3-17, the control system 300 mayinclude a first shift valve 346, a second shift valve 348, and a thirdshift valve 350. The function of each shift valve will be describedbelow, particularly with respect to each range and fault range. Thesecond shift valve 348, however, may directly feed clutch pressure tothe second torque-transmitting mechanism, C2, and the fifthtorque-transmitting mechanism, C5. In this control system 300, only oneof C2 and C5 is applied for a given range.

Each of the shift valves may move between a stroked position and ade-stroked position. To do so, the first shift solenoid 330 may beconfigured to actuate the first and second shift valves, and the secondshift solenoid 332 may be configured to actuate the third shift valve350. The manner in which each shift valve is actuated in a given rangewill be further described below.

Another valve shown in the control system 300 of FIG. 3 includes a boostvalve 354. The boost valve 354 and second trim valve 314 may controlhydraulic fluid to C2 and C5, which will be described below.

The control system 300 further includes a first pressure switch 356, asecond pressure switch 358, a third pressure switch 360, and a fourthpressure switch 362. Each pressure switch may be actuated between afirst position and a second position. In the first position, thepressure switch is pressurized, and in the second position the pressureswitch is not pressurized. Based on the position, the controller candetect different valve positions and gains throughout the control system300.

In the present disclosure, the control system 300 is such that twotorque-transmitting mechanisms are applied. Referring to FIG. 21, forexample, a mechanization table 2100 of a multispeed transmission isprovided. In this table 2100, a plurality of forward ranges, neutral anda reverse range are shown. In this embodiment, there are nine forwardranges, but there may be a different number of forward and reverseranges for other embodiments. This disclosure is not limited to anynumber of forward and reverse ranges.

The columns of the mechanization table 2100 of FIG. 21 furtherillustrate the different solenoids. As shown, the shift solenoids 330,332 are shown as normally-low solenoids (“N/L”) as well as the fourthpressure control solenoid 320 and the fifth pressure control solenoid324. The first pressure control solenoid 308, the second pressurecontrol solenoid 312, and the third pressure control solenoid 316 areshown as normally-high solenoids (“N/L”) in the table 2100. In thetable, a zero (“0”) identifies as the solenoid as being off or notreceiving current, whereas a one (“1”) indicates the solenoid as beingon or receiving current (i.e., energized). The pressure controlsolenoids indicate which clutch is available in each range for beingapplied. The following table illustrates one embodiment in which atleast two torque-transmitting mechanisms are engaged or applied:

Steady Engaged Torque- Engaged Torque- State Range TransmittingMechanism Transmitting Mechanism Reverse C5 C3 Neutral C5 — 1^(st) C5 C62^(nd) C5 C1 3^(rd) C1 C6 4^(th) C1 C4 5^(th) C1 C3 6^(th) C1 C2 7^(th)C2 C3 8^(th) C2 C4 9^(th) C2 C6

The mechanization table 2100, however, illustrates other clutches thatmay be available for any given range. For example, in 5th range, C1 andC3 are applied to achieve this range. However, C4 and C6 are alsoavailable if the requisite trim system was triggered to allow fluid toflow to the respective clutch. For instance, if the fifth pressurecontrol solenoid 324 is energized in fifth range, the fifth trim valve326 may be stroked to allow pressure to fill and apply C6. Thus, themechanization table 2100 illustrates the clutches that are applied andalso the clutches that may be available depending upon the position of avalve or state of a solenoid. This is further described with respect tohydraulic default ranges below.

In the mechanization table 2100 of FIG. 21, it is noted that the firstpressure control solenoid 308 may control C1 between an applied andunapplied state, the second pressure control solenoid 312 may controleither C2 or C5, as discussed above, between an applied and unappliedstate, and the third pressure control solenoid 316 may control C3between an applied and unapplied state. Each of these three solenoids isa normally-high solenoid, and thus if electrical power is lost and nocurrent is sent to these solenoids, each solenoid still outputs fullpressure to the respective trim valve. If hydraulic pressure is receivedat the respective trim valve, then with the solenoid outputting fullpressure, the respective clutch or brake (C1, C2/C5, and C3) may beapplied.

Moreover, the table 2100 further illustrates that the fourth pressurecontrol solenoid 320 may control C4 between an applied and unappliedstate, and the fifth pressure control solenoid 324 may control C6between an applied and unapplied state. Both of these two solenoids,however, are normally-low solenoids and therefore output zero pressurewhen the solenoid receives no current. In this embodiment, if power islost and either C4 or C6 is applied, the respective pressure controlsolenoid discontinues sending pressure to the respective trim valve andthe clutch or brake is unapplied. Thus, with respect to C4 and C6, bothtorque-transmitting mechanisms may be triggered from their applied tounapplied state if electrical power is lost and no current is sent totheir respective pressure control solenoid.

It is further shown in the mechanization table 2100 of FIG. 21 thedifferent hydraulic default ranges for each of the forward, neutral andreverse ranges. In the control system 300 of FIG. 3, and the multispeedtransmission to which the control system 300 controls, there are acombination of two clutches or brakes applied per range, except forneutral. In neutral, only one clutch or brake is applied. However, thetable 2100 identifies other clutches or brakes that may be applied. Forexample, in 1^(st) range, C5 and C6 are normally applied. In the table,however, it is further shown that torque-transmitting mechanisms C1, C3,and C4 are available to be applied if the controller operably energizesor de-energizes the necessary solenoids. The same may be true for otherranges, such as 8^(th) range where C2 and C4 are applied but C3 and C6are available if the controller energizes the third and fifth pressurecontrol solenoids.

As shown in the table, the control system 300 includes a neutral defaultrange, a low default range (i.e., 5^(th) range) and a high default range(i.e., 7^(th) range). In neutral, the control system 300 may beoptimally setup such that if electrical power is lost, C5 is unappliedand C3 is applied to achieve a C3N default range (i.e., C3 neutral). Asdiscussed above, C3 is controlled by the third pressure control solenoid316, and when electrical power is lost, the third pressure controlsolenoid 316 still outputs full pressure to stroke the third trim valve318 and allow hydraulic pressure at the trim valve to fill and apply C3.This will be further described with respect to FIGS. 15-17. The mannerin which the low and high default ranges are achieved will also bedescribed below with respect to FIGS. 15-17. For purposes of thisdisclosure, however, the control system 300 is capable of defaultinginto three different conditions or ranges if power is lost, and eachcondition or range is better able to protect the transmission from beingdamaged.

In the control schematics of FIGS. 3-17, the trim valves and shiftvalves are shown without much detail, i.e., with respect to length anddiameter. Referring to FIG. 18, one non-limiting example of a valve 1800is shown. In this example, the valve 1800 may be an example of the firstshift valve 346. Here, the valve 1800 has an overall length withdifferent portions and diameters (or widths). The valve 1800 may includea stem or body 1802. Moreover, along the length of the valve 1800, thereis a first valve portion 1804, a second valve portion 1806, a thirdvalve portion 1808, a fourth valve portion 1810, a fifth valve portion1812, and a sixth valve portion 1814. In this example, the fourth valveportion 1810 has a diameter, D1, which is greater than the diameter ofthe first, second and third portions. Further, the fifth valve portion1812 has a diameter, D2, which is greater than D1, and therefore thefifth valve portion 1812 has a greater diameter than the first, second,third, and fourth valve portions. Yet further, the sixth valve portion1814 has an overall diameter, D3, that is greater than diameters D1 andD2. As such, the sixth valve portion D3 is the largest diameter of thevalve 1800.

In FIG. 18, the valve 1800 is also shown as including three interlock orlatch locations. An interlock or latch may refer to hydraulicallyholding a valve in position regardless of solenoid pressure. Thus, solong as hydraulic pressure is available at the interlock or latch, thevalve is unable to move. This is particularly relevant with the shiftvalves. Although not shown in this disclosure, each shift valve may bedisposed within a pocket of a valve body or the like along with a returnspring. The spring may have a spring force that counteracts against theshift valve stroking from its de-stroked position to its strokedposition. With a latch or interlock, however, sufficient hydraulicpressure may act against a valve portion to hold the valve in place evenif the solenoid pressure at the head of the valve is removed. In FIG.18, a first interlock 1816 is shown on the fourth valve portion 1810, asecond interlock 1818 is shown on the fifth valve portion 1812, and athird interlock 1820 is shown on the sixth valve portion 1814. Thus, onthe first shift valve 346, there may be three interlocks.

With respect to the interlocks, the first shift valve may be referred toas the range valve. During operation, hydraulic fluid acting on one ofthe interlocks may allow the range valve to stay in a certain range.This is also true for neutral. Moreover, the interlocks on the firstshift valve allow for the control system to default to the necessarydefault ranges as shown in FIG. 21.

The interlocks are based on a force balance along the valve. Ifhydraulic pressure is acting against the first interlock 1816, and moreparticularly against diameter D1, this pressure may be greater than thespring force counteracting the hydraulic pressure. The force may bedetermined based on a conventional means, i.e., the amount of pressuremultiplied by the area of the valve portion. With respect to the firstshift valve 346, the interlocks may maintain the valve in its strokedposition based on which torque-transmitting mechanism is engaged. Infifth range, for example, there may not be any control pressure from thefirst shift solenoid, which under certain circumstances would de-strokethe first shift valve 346. However, hydraulic pressure acting on thethird interlock 1820 may keep the valve stroked and allow clutchpressure to fill and apply C1. This is only one of several examples ofthe interlock keeping a shift valve in a desired position for aparticular range. In another example, C2 is applied and hydraulicpressure flows to the first shift valve 346 and may act on the secondinterlock 1818 to maintain the valve in its stroked position.

Referring to FIG. 19, one example of the second shift valve 348 isshown. Here, a valve 1900 representative of the second shift valve 348may include a length partially defined by a valve stem or body 1902, afirst valve portion 1904, a second valve portion 1906, a third valveportion 1908, a fourth valve portion 1910, a fifth valve portion 1912,and a sixth valve portion 1914. A shown in FIG. 19, the first, secondand third valve portions may include a diameter, D4, whereas the fourth,fifth, and sixth valve portions may include a diameter, D5. Here, D5 isgreater than D4, thereby forming or defining an interlock 1916 on thelarger valve portions. In addition, at one end of the valve 1900 is asecond interlock 1918. The second interlock 1918 may maintain the secondshift valve 348 in a de-stroked position via clutch pressure for C5.Thus, even if control pressure is provided at the opposite end of thesecond shift valve 348 via the first shift solenoid 330, hydraulicpressure at the second interlock 1918 may be enough to keep the valvefrom stroking.

With respect to the first interlock 1916 on the valve 1900, this may beuseful when operating in a higher range (e.g., 6^(th)-9^(th) ranges) andC2 is applied. As previously noted, the second shift valve 348 candictate whether C2 or C5 is applied. In other words, this shift valvemultiplexes, which will be described below. In 7^(th) range (FIG. 12),however, the first shift solenoid 330 may supply control pressure to oneend of the second shift valve 348 to move it to its stroked position.Hydraulic pressure that fills and applies C2 may also flow inbetween thethird valve portion 1908 and fourth valve portion 1910, and due to thefirst interlock 1916, the second shift valve 348 may be hydraulicallyheld in place regardless of whether the first shift solenoid 330 sendscontrol pressure or not. This again is due to hydraulic pressure actingon a differential area of the valve 1900 due to a force balance acrossthe valve. Thus, the interlocks are useful for establishing the defaultranges (FIGS. 15-17), which will be further addressed below.

As described above, the second shift valve 348 may multiplex. First,however, in the control system 300 of FIG. 3, each clutch or brake hassomething to hydraulically fill and apply it. For C1, C3, C4, and C6,there is a trim system for filling and applying each torque-transmittingmechanism. In a multiplex system, a single trim system is used tohydraulically apply more than one torque-transmitting mechanism. Withrespect to C2 and C5, the second shift valve 348, the second pressurecontrol solenoid 312, the second trim valve 314, and the boost valve 354may be used for hydraulic control. In one example, if the second shiftvalve 348 is de-stroked (i.e., stroked up), C5 may be hydraulicallycontrolled (i.e., reverse, neutral, 1^(st) and 2^(nd) ranges). On theother hand, if the second shift valve 348 is stroked (i.e., strokeddown), C2 may be hydraulically controlled (i.e., 6^(th)-9^(th) ranges).Thus, if hydraulic pressure is available at the second shift valve, theneither C2 or C5 may be hydraulically applied based on a position of theshift valve.

With the second shift valve 348 functioning as a multiplex system, lesshardware (such as a trim solenoid and trim valve) is necessary for thecontrol system. Moreover, the multiplex system effectively “locks out”or prevents both C2 and C5 from applying at the same time. This may beimportant, for example, to protect the integrity of the transmissionfrom potential damage due to a locked output. In a higher speed when C2is applied, there may be potential damage to the transmission if C5 isapplied at the same time. Thus, the second shift valve 348 may allowonly either C2 or C5 to hydraulically apply, but not the other.

Referring now to FIG. 20, a representative valve 2000 for the thirdshift valve 350 is shown. The valve 2000 is only one example of thethird shift valve 350, as it may differ in other examples. In FIG. 20,however, the valve 2000 may include a length defined by a valve stem orbody 2002, a first valve portion 2004, a second valve portion 2006, athird valve 2008, a fourth valve portion 2010, and a fifth valve portion2012. In this example, each valve portion has the same diameter orwidth. Thus, there are no interlocks or latches formed with this valve2000. However, in other embodiments, one or more of the valve portionsmay have a different diameter or width to form an interlock or latch.

In this disclosure, the third shift valve 350 may be referred to as apower valve. The power valve is able to block hydraulic pressure fromapplying C1. It does so be effectively blocking a main pressure feed tothe first pressure control trim system, e.g., the first trim valve 310.In 7^(th) range, for example, the third shift valve 350 is able to blockmain pressure from reaching the first trim valve 310 (FIG. 12). In FIG.12, main pressure is supplied by the pressure source 302 and it can flowto the third shift valve 350. As noted above, the third shift valve 350may not include any interlocks or latches, and therefore its positionmay be controlled by control pressure from the second shift solenoid332. In FIG. 12, however, the second shift solenoid 332 may bede-energized such that it does not output any control pressure. Withoutany control pressure acting against the third shift valve 350, the thirdshift valve 350 may be de-stroked. In its de-stroked position, mainpressure from the pressure source 302 is blocked (e.g., by the secondvalve portion 2006). Thus, from FIG. 12 and in 7^(th) range, C1 is notapplied due to the third shift valve 350 blocking pressure from reachingthe first trim valve 310. The same may be true in 8^(th) and 9^(th)ranges as well.

The third shift valve 350 is also able to block hydraulic fluid fromflowing to the second trim system, i.e., the second trim valve 314.Moreover, the third shift valve 350 effectively blocks flow fromreaching the second shift valve 348 as well. However, in 7^(th) range,for example, the interlock on the second shift valve 348 maintains thevalve in a position which fills and applies C2. As will be discussedbelow, the second shift valve 348 and the third shift valve 350 also maybe controlled such that hydraulic pressure is not fed to all three ofthe trim valves actuated by the normally-high solenoids. If clutchpressure was fed to all three trim valves, then C1, C3 and one of C2 orC5 would apply thereby possibly causing damage to the transmission. Thecontrol system 300 therefore controls the position and movement of thesecond and third shift valves to block flow from one or more of the trimvalves to prevent this from happening.

Another feature of this disclosure is the control of the range valve,i.e., the first shift valve 346. The range valve may be operablycontrolled via a shift-by-wire control system. In other words, a vehicleoperator may push a button, turn a knob, trigger a switch or some otheroperation to send an instruction to the controller to select a range ofthe transmission system. In turn, the controller may energize one ormore solenoids to electrically actuate the control system 300 to adesired range. Thus, in the shift-by-wire control system, there is nomanual linkage for controlling a detent or the like for manuallycontrolling the transmission system to a certain range. In thisdisclosure, the controller therefore can control the position of therange valve (i.e., first shift valve 346) in order to select a range orshift to a different range.

In an alternative embodiment, the range valve may be replaced by a threeposition manual valve that is manually actuated by a shift linkage. Inother words, a cable or other linkage may be installed for manuallycontrolling the transmission into range.

Turning now to the specifics of FIG. 3, the control system 300 is shownoperating in reverse. In other words, the controller has received acommand from an operator to control the transmission in reverse via ashift-by-wire system, or an operator has controlled a shift linkage tocontrol the transmission in reverse. In any event, main pressure issupplied by the pressure source 302 to the control system 300. As shownin FIG. 21 and described above, C3 and C5 are engaged in reverse. Toachieve this, main pressure is fed to the third trim valve 318 and thecontroller energizes the third pressure control solenoid 316 to move thethird trim valve 318 to its stroked position. In this manner, hydraulicfluid is able to fill and apply C3 in reverse.

For C5, it is first worth noting that the first shift solenoid 330 isde-energized and the second shift solenoid 332 is energized. Thus, thefirst and second shift valves are in their respective de-strokedpositions, and the third shift valve 350 is in its stroked position(i.e., since the second shift solenoid 332 controls the third shiftvalve 350). With the third shift valve 350 in its stroked position, mainpressure is able to flow through the third shift valve 350 and throughthe second shift valve 348, as shown in FIG. 3. As main pressure flowsthrough the second shift valve 348, it flows directly to the second trimvalve 314. The controller may energize the second pressure controlsolenoid 312 in order to move the second trim valve 314 to its strokedposition, and with main pressure at the second trim valve 314, hydraulicfluid is able to flow through the second trim valve 314 and back throughthe second shift valve 348 to fill and apply C5.

C5 pressure flows back through second shift valve 348 once it is appliedas shown in FIG. 3. In particular, C5 pressure may flow and apply apressure force against one end of the second shift valve 348 to maintainthe valve in its position. In this instance, an interlock may be formedon one end of the second shift valve 348.

C5 pressure also flows back to the boost valve 354 and is able to forceor maintain the boost valve 354 in its de-stroked position. The functionand use of the boost valve will be described further below.

In reverse, the other torque-transmitting mechanisms are unapplied.First, main pressure flows to the first shift valve 346, but with thefirst shift valve 346 de-stroked, main pressure is effectively blockedby the first shift valve 346. The second shift valve 348 also blocksmain pressure via one of its valve portions. As a result, there is nomain pressure being fed to the first trim valve 310. Regarding C2, as wedescribed previously, the second shift valve 348 multiplexes and allowsonly one of C2 or C5 to be applied. In reverse, the second shift valve348 may be in its de-stroked position so that only C5 is applied.

With regards to C4 and C6, the controller is not sending any current toeither the fourth pressure control solenoid 320 or the fifth pressurecontrol solenoid 324, and therefore the respective trim valves arede-stroked. With respect to the fourth trim valve 322, it is shown inFIG. 3 that main pressure flows to the fourth trim valve 322. But, withthe fourth trim valve 322 de-stroked, main pressure is blocked by thetrim valve and unable to fill and apply C4. Moreover, the second shiftvalve 348 blocks main pressure from feeding the fifth trim valve 326,and if even pressure was fed to the fifth trim valve 326, the fifthpressure control solenoid 324 is de-energized. Thus, the fifth trimvalve 326 is de-stroked and no hydraulic fluid can fill and apply C6.

With reverse described above and shown in FIG. 3, the control system 300is further capable of controlling the transmission from reverse toneutral in the event of a power loss to the system. This is shown inFIG. 15. In this embodiment, C3 remains applied and C5 is exhausted.During a power loss event, the normally-low solenoids (i.e., the fourthpressure control solenoid 320 and fifth pressure control solenoid 324)are de-energized and thus neither C4 nor C6 are capable of being filledand applied. Moreover, the first shift solenoid 330 and the second shiftsolenoid 332 are de-energized and therefore the first shift valve 346,the second shift valve 348, and the third shift valve 350 arede-stroked. Lastly, the normally-high pressure control solenoids 308,312, and 316 output full pressure during a power-off event.

As shown in FIG. 15, main pressure is supplied from the fluid source 302to the third trim valve 318, the fourth trim 322, the first shift valve346, and the third shift valve 350. With the third pressure controlsolenoid 316 outputting full pressure to the third trim valve 318,hydraulic fluid is able to continue filling and applying C3. Thus, fromreverse to default neutral, C3 remains applied. C4 and C6 remainunapplied because they are normally low solenoids. Even though the firstand second pressure control solenoids are outputting full pressure tostroke the first trim valve 310 and the second trim valve 314, the firstshift valve 346 and the third trim valve 350 are de-stroked andeffectively block main pressure from flowing to either trim valve.Further, with the first and third shift valves de-stroked, there is nohydraulic fluid for feeding the second shift valve 348. Without anyfluid passing through any of the shift valves or the second trim valve314, neither C2 nor C5 are filled and applied. Thus, in the power-offevent of FIG. 15, only C3 is applied and the transmission defaults to aC3 Neutral state.

During the power-off event from reverse to C3 Neutral, C5 is exhausted.In one embodiment, C5 may be considered a large clutch or brake thatrequires a substantial amount of fluid to apply it. During coldtemperatures, the viscosity of the fluid may be such that the fluid doesnot exhaust quickly from C5. A first exhaust path for C5 is through thesecond shift valve 348 and a second exhaust path is through the secondtrim valve 314. In both cases, the fluid travels a long distance toreach an exhaust outlet (identified in FIGS. 3-17 as a small circle withan X circumscribed). Due to its higher viscosity at low temperatures, itcan be difficult to quickly exhaust C5 through either the first orsecond exhaust paths.

As shown in FIG. 15, however, a third and shorter exhaust path may beprovided for more quickly exhaust C5. Here, the third exhaust path isdefined from C5 through the third shift valve 350 and to the exhaustbackfill valve 342 where fluid is exhausted to the reservoir 206. WhenC5 is released, hydraulic fluid is able to flow through any of thesethree fluid paths to exhaust, and the third exhaust path is shorter thanthe first and second exhaust paths thereby allowing fluid to morequickly exhaust at colder temperatures.

Referring to FIG. 4, the control system 300 is shown controlling thetransmission in neutral or park. In this illustrated embodiment, C5 isengaged and the other torque-transmitting mechanisms are disengaged. Toget this arrangement, main pressure continues to be supplied by thepressure source 302. Here, the controller energizes the second pressurecontrol solenoid 312 to move the second trim valve 314 to its strokedposition. The other pressure control solenoids are de-energized, andtherefore C1, C3, C4 and C6 are disengaged. The first shift solenoid 330is de-energized, and thus the first shift valve 346 and the second shiftvalve 348 are de-stroked. The second shift solenoid 332, however, isenergized and control main pressure is fed to one end of the third shiftvalve 350 to move it to its stroked position.

Main pressure is fed to the third trim valve 318 and the fourth trimvalve 322, but with each trim valve de-stroked there is no pressurefilling either C3 or C4. With the first shift valve 346 de-stroked inFIG. 4, main pressure is blocked by one portion (e.g., the third valveportion 1808) of the first shift valve 346 to prevent hydraulic fluidfrom being directed to the first trim valve 310. Thus, C1 is unappliedfor at least this reason (as well as the first trim valve 310 isde-stroked and would otherwise block the fluid).

With the third shift valve 350 being stroked by the control mainpressure being fed by the second shift solenoid 332, main pressure isable to flow through the third shift valve 350 to the second trim valve314 via the second shift valve 348. In particular, while the secondshift valve 348 is de-stroked, hydraulic fluid may be able to flowbetween the first portion 1904 and the second portion 1906 of the valve.As fluid flows to the second trim valve 314, the second pressure controlsolenoid 312 is energized by the controller to move the second trimvalve 314 to its stroked position. As a result, fluid is able to flowback through the second shift valve 348 and fill and apply C5.

In the event of a power loss, the controller is unable to control any ofthe solenoids. As a result, when the transmission is in neutral as shownin FIG. 4, the energized second shift valve 332 is de-energized andtherefore the third shift valve 350 moves from its stroked position toits de-stroked position. Once the third shift valve 350 moves to itsde-stroked position as shown in FIG. 15, main pressure is blocked by theshift valve (e.g., by the second valve portion 2006) and hydraulic fluidno longer flows through the second shift valve 348 to the second trimvalve 314. Thus, even though the second pressure control solenoid 312 isa normally-high solenoid and outputs full pressure, there is nohydraulic fluid available to continue filling and applying C5. Thus, C5exhausts through any or all of its three exhaust paths, as describedabove.

As shown in FIG. 15, main pressure continues to flow to the third andfourth trim valves. With the third pressure control solenoid 316outputting full pressure to move the third trim valve 318 to its strokedposition, fluid is able to fill and apply C3. The same is not the casewith C4, as the fourth pressure control solenoid 320 remainsde-energized and the fourth trim valve 322 therefore blocks mainpressure from filling C4. As a result, when the transmission is inneutral or park and power is lost, C5 is exhausted and C3 is applied sothat the control system 300 defaults to the C3 Neutral state.

One of the features of this default C3 Neutral state is that the rangevalve, i.e., the first shift valve 346, is in its de-stroked positionand blocks fluid from flowing to the first trim valve 308 and the fifthtrim valve 326. Moreover, the third shift valve 350 is de-stroked andblocks fluid from flowing to the second trim valve 314. Thus, eventhough the first pressure control solenoid 308 and the second pressurecontrol solenoid 312 output full pressure to their respective trimvalves, the first shift valve 346 is disposed to block the supply ofhydraulic fluid to fill C1 and C6, and the third shift valve 350 isdisposed to block the supply of hydraulic fluid to fill C5. As a result,the transmission is effectively prevented from shifting into eitherreverse or a forward range due to the position of the first shift valve346 and third shift valve 350.

Another aspect of the present disclosure is the ability to detect valveposition and default ranges with the pressure switches. With shiftvalves, it is desirable to be able to detect the position of each shiftvalve to ensure hydraulic fluid is being directed to the correct pathand prevent an unwanted torque-transmitting mechanism from being filledand applied. In the present disclosure, that is further the case withthe second shift valve which multiplexes and controls both C2 and C5.Each pressure switch in the control system 300 is capable of beingpressurized by control main pressure and moving between a first positionand a second position. Each pressure switch is in electricalcommunication with the controller to provide feedback to the controllerbased upon the position of the switch. As will be described below,pressure switches are able to communicate additional information to thecontroller including low or high gain and a position of the boost valve354.

In the control system 300 of FIGS. 3-17, the first pressure switch 356is capable of detecting the position of the first shift valve 346, thesecond pressure switch 358 is capable of detecting the position of thesecond shift valve 348, and the third pressure switch 360 is capable ofdetecting the position of the third shift valve 350. The fourth pressureswitch 362 is able to detect the position of the third trim valve 318,and thus whether C3 is engaged or not. If the transmission is operatingin a steady state neutral with C5 applied, and the fourth pressureswitch 362 detects movement of the third trim valve 318 from itsde-stroked position to its stroked position (and thus C3 will beapplied), the controller can detect this movement via the fourthpressure switch 362.

In this embodiment, the fourth pressure switch 362 may change state orposition as the third trim valve 318 moves to a position near itshalfway point between its fully stroked and fully de-stroked positions.In this instance, the fourth pressure switch 362 may be exhausted whenthe third trim valve 318 is de-stroked. However, as the third trim valve318 moves to its stroked position, control main pressure fills andpressurizes the fourth pressure switch 362 thereby sending a signal tothe controller indicative of this event. As noted above, reverse isachieved when C3 and C5 are applied. Thus, in neutral with C5 applied,the controller receives the message from the fourth pressure switch 362indicating that C3 will begin filling shortly as the third trim valve318 moves closer to its stroked position. If the controller determinesthat reverse is undesirable, it can control C5 to exhaust and default tothe C3 Neutral state to prevent reverse. Thus, the fourth pressureswitch 362 provides a good fault detection when operating in neutral.

The controller is also able to monitor the different pressure switchesto determine if a particular valve strokes. For instance, if the firstshift valve 346 moves to its stroked position, the first pressure switch356 may detect this movement and communicate the same to the controller.In this way, the controller is better able to control the control system300 and ensure the proper range is selected based on operator input.This is particularly true with the shift-by-wire system whereby theoperator may select a button to control the transmission from park to afirst forward range. In this event, the controller is able to detect theshift in range by monitoring the pressure switches.

Another feature of the present disclosure is the use of the pressureswitches with the multiplexing function of the second shift valve 348.As previously described, the second shift valve 348 is able to controlwhether C2 or C5 is engaged. If the second shift valve is de-stroked,then C5 is engaged and C2 is exhausted. If the second shift valve 348 isstroked, then C2 is engaged and C5 is exhausted. Depending on theposition of the second shift valve 348, the second pressure switch 358is either pressurized or exhausted. In one embodiment, the secondpressure switch 358 is exhausted when the second shift valve 348 isde-stroked, and the second pressure switch 358 is pressurized when thesecond shift valve 348 is stroked. In an alternative embodiment, thesecond pressure switch 358 is pressurized when the second shift valve348 is de-stroked, and the second pressure switch 358 is exhausted whenthe second shift valve 348 is stroked. In any event, the second pressureswitch 358 may change state between exhausted and pressurized when thesecond shift valve 348 reaches approximately halfway between the strokedand de-stroked positions. Moreover, the controller is able to detect theposition of the second shift valve 348 and whether either C2 or C5 iscapable of being filled and applied based whether the second pressureswitch 358 is exhausted or pressurized.

Turning to FIG. 5, one embodiment of the control system 300 controllingthe transmission in a first forward range is shown. In this embodiment,main pressure is supplied by the pressure source 302 to the system 300.The controller may send current to the first shift solenoid 330 and thesecond shift solenoid 332 in order to stroke the first shift valve 346and the third shift valve 350. Control main pressure is fed from the twoshift solenoids to all three shift valves, but only the first shiftvalve 346 and the third shift valve 350 move to their stroked positions.While control main pressure is fed to the second shift valve 348, thesecond shift valve 348 does not move from its de-stroked position. Asdescribed above, C5 is applied in neutral, and in the process hydraulicfluid flows from the second trim valve 314 through one end of the secondshift valve 348 to fill and apply C5. As the fluid flows through thesecond shift valve 348, it is able to hydraulically hold or maintain thevalve in this position. In other words, one of the aforementionedinterlocks 1918 holds the valve in position even though control mainpressure from the first shift solenoid 330 tries to move the secondshift valve 348. Thus, in this first forward range (or simply firstrange), C5 remains applied from neutral.

Main pressure flows to the third trim valve 318 and the fourth trimvalve 322 according to its normal flow path. Here, the controller doesnot energize the third pressure control solenoid 316 or the fourthpressure control solenoid 320, and thus the respective trim valves blockmain pressure from feeding either C3 or C4. In the same way, mainpressure is fed through the shift valves to the first trim valve 310,but the controller also does not energize the first pressure switch 308and C1 therefore is unable to apply due to the first trim valve 310blocking main pressure. Lastly, with hydraulic fluid applying C5 andmaintaining the second shift valve 348 in its de-stroked position, thesecond shift valve 348 prevents fluid from filling and applying C2.Thus, C1-C4 are not applied in first range.

In the illustrated embodiment of FIG. 5, the controller does sendcurrent to energize the fifth pressure control solenoid 324. In doingso, the fifth pressure control solenoid 324 is able to move the fifthtrim valve 326 and the boost plug 328 to allow fluid to fill C6.Hydraulic fluid supplied by the pressure source 302 flows to the firstshift valve 346, and with the first shift valve 346 moved to its strokedposition, fluid is able to flow to the fifth trim valve 326 and fill C6.C6 is thus applied in first range.

As described above, the second pressure switch 358 is able tocommunicate with the controller the position of the second shift valve348. Thus, the controller may send current to the first and second shiftsolenoids, and based on feedback from the first pressure switch 356 thecontroller is able to detect movement of the first shift valve 346 toits stroked position. When shifting from neutral to first range,however, C5 remains applied and the second shift valve 348 does notmove. The controller is able to detect that the interlock acting on thesecond shift valve 348 is working properly so long as the secondpressure switch 358 remains exhausted, for example (assuming it isexhausted in neutral). In this manner, the pressure switch is able tocommunicate when an interlock is active.

Similarly, an interlock may exist on the other end of the second shiftvalve 348. Here, this interlock is not active in first range, but it isin seventh range, eighth range and ninth range. Control main pressurefed from the third shift valve 350 acts on a top end of the second shiftvalve 348 to hydraulically hold the second shift valve 348 in itsstroked position. As such, the second pressure switch 358 may bepressurized with the valve in this position, and the controller is ableto detect the interlock being active based on the valve position.

In FIG. 6, the control system 300 is shown hydraulically operating thetransmission in another embodiment of first range. In FIG. 5, the TCCsolenoid 304 is de-energized such that main pressure is blocked by theTCC trim valve 306. In this embodiment, there is no lockup pressuresupplied to the torque converter 202 of the transmission system 200. InFIG. 6, however, the controller may send current according to any knownmeans for energizing the TCC solenoid 304 and moving the TCC trim valve306 to its stroked position. As shown in FIG. 6, lockup clutch pressuremay be fed from the TCC trim valve 306 to the converter flow 214. Fluidmay flow from the converter flow 214 via the converter in path 222 tohydraulically apply a lockup clutch of the torque converter 202. Themanner and operation of the lockup clutch may be according to any knownmeans. Moreover, when the controller energizes or de-energizes the TCCsolenoid 304 may be according to any known algorithm or process based onspeed, torque, range, etc. It is noted that in the embodiment of FIG. 6,the manner in which C5 and C6 are applied is substantially the same.

In the event of a power loss in first range, current is no longer sentto energize the fifth pressure control solenoid 324, the first shiftsolenoid 330 or the second shift solenoid 332. As a result, the fifthtrim valve 326 de-strokes and blocks the fluid path to C6. C6 thereforeexhausts. This is shown in FIG. 16 as well. With the second shiftsolenoid 332 being de-energized, the third shift valve 350 de-strokesand blocks main pressure from feeding the second trim valve 314. As aresult, hydraulic fluid is no longer supplied to C5 and C5 exhausts.Thus, no fluid is supplied to either C5 or C6, which previously wereboth applied in first range.

As previously described, however, the first and third pressure controlsolenoids are normally-high solenoids which output full pressure in apower-off event. With main pressure feeding the third trim valve 318, C3is filled and applied when there is a loss of power. Also, with thefirst pressure control solenoid 304 outputting pressure to the firsttrim valve 306, main pressure via the first shift valve 346 is able tofill and apply C1. Thus, when the control system 300 is operating infirst range and there is a loss of electrical power, the control system300 defaults to fifth range by exhausting C5 and C6 and applying C1 andC3.

In another aspect of the present disclosure, the control system 300 isable to control gain actuation via the boost plug 328. In this aspect,the control system 300 is able to provide a low clutch control gain inninth range and a high clutch control gain in third range. To do so, theboost plug 328 may be operably controlled to adjust gain.

Before addressing C6, gain control may be relevant when atorque-transmitting mechanism may need different pressure for differentranges. For example, in one high range, the mechanism may only need 80psi, but the same mechanism may need 230 psi in a lower range tomaintain torque. To achieve these different pressures, the gain may beadjusted on the clutch trim system. In addition, a pressure switch maybe used to detect high or low gain and communicate this to thecontroller.

C6 is applied in first, third and ninth ranges by the fifth pressurecontrol solenoid 324 and the fifth trim valve 326. In first range, C6may need up to 250 psi, for example, to hold torque, whereas in ninthrange C6 may only need approximately 80 psi. These pressures are onlyprovided as examples and may vary in different embodiments. Thus, thesepressures are provided as non-limiting to the scope of this aspect ofthe present disclosure.

In first range, torque can be much greater than in ninth range. In ninthrange, controllability and shift quality may be important. Thus, infirst range, the gain may be set at 2.78 to achieve a higher clutchpressure, and in ninth range the gain may be set at 1.6. Again, thesegain values are non-limiting and are only provided as an example of lowand high gain values. Gain adjustment is available on a trim valve dueto a differential area on one or more portions of the valve. This ispartly described above with respect to the shift valves and theinterlocks.

To take this example further, suppose a pressure control solenoid isable to output 1000 kPa. At a low range, the 2.78 gain allows the trimsystem to output up to 2780 kPa. Similarly, at a higher range, the 1.6gain allows the trim system to output up to 1600 kPa. Thus, there is arelationship between the output pressure of the solenoid (usuallydictated by control pressure or control main pressure) and the actualclutch pressure. Shift quality is better achieved at a lower clutchpressure, but torque requirements at the lower ranges may requiregreater clutch pressure to reduce or prevent clutch slippage.

In addition to the above, the pressure switches can also communicate tothe gain level to the controller. With regards to the fifth trim valve326, the second pressure switch 358 is able to detect its position. Infirst range (FIGS. 5 and 6) and third range (FIG. 8), output pressurefrom the fifth pressure control solenoid 324 forces the fifth trim valve326 and boost plug 328 in a downward or stroked position, where“downward” is only relative to how the valve and plug are shown in thedrawings. In FIG. 8, for example, there is no control main pressurizingthe second pressure switch 358. Based on this, the controller is able todetect that the fifth trim system is set at its high gain level.

In ninth range (FIG. 14), however, control main pressure is fed topressurize the second pressure switch 358. The same control mainpressure is fed to the boost plug 328, where the hydraulic fluid is ableto flow through the channel 344 defined in the boost plug 328. As aresult, hydraulic fluid separates the boost plug 328 from the fifth trimvalve 326 and moves the plug 328 toward the fifth pressure controlsolenoid 324. In this condition or state, the trim system is at a lowergain value and the second pressure switch 358 detects and communicatesthis to the controller.

The high/low gain actuation of the fifth trim system allows for lowerclutch pressure control in ninth range to improve shift quality andcontrollability, and higher clutch pressure control in first and thirdranges to reduce or prevent clutch slippage. This further allows forfull engine torque clutch control during a neutral to first range shiftdue to the higher gain, and there is no need for any additional hardwareor actuators to detect the gain setting. The second pressure switch 358is therefore capable of detecting the position of the second shift valve348 and the gain setting of the fifth trim valve 326.

Referring to FIG. 7, a second forward range, or simply second range, isillustrated. Here, the control system 300 is able to selectively controlhydraulic fluid to fill and apply C1 and C5. In first range, C5 and C6are applied, and so to transition or shift to second range, C6 isexhausted and C1 is applied.

To shift to second range, the controller may energize the second shiftsolenoid 332 which pressurizes and strokes the third shift valve 350.The first shift solenoid 330 may not receive current in second range,and thus control main pressure is not fed to the head of either thefirst or second shift valves. However, the timing of this may dependupon the embodiment. For example, the controller may delay de-energizingthe first shift solenoid 330 until the upshift from first range tosecond range is complete. Once the shift is complete, the controller maythen de-energize the first shift solenoid 300. Thus, while theillustrated embodiment of FIGS. 3-17 may show one of the two shiftsolenoids being energized or de-energized, the controller may controlthe timing of when the respective solenoid is energized and de-energizedto allow for various shifts of the transmission to be completed.Software, control algorithms, calibration methods, instructions, tables,graphs, and the like may be stored in a memory unit 144 of thecontroller 142 and executed according to any known means to control thetiming of sending current to any of the solenoids in the control system300.

In any event, in second range, the controller energizes the firstpressure control solenoid 308 and the second pressure control solenoid312 in order to move the first trim valve 310 and the second trim valve314 to their respective stroked positions. The third pressure controlsolenoid 316, the fourth pressure control solenoid 320, and the fifthpressure control solenoid 324 are de-energized, and their respectivetrim valve is in its de-stroked position to block hydraulic fluid fromfilling and applying C3, C4, and C6 respectively.

As for the flow of hydraulic fluid through the control system 300, mainpressure is again fed by the pressure source 302 to the first shiftvalve 346 and third shift valve 350 as shown in FIG. 7. Hydraulic fluidflows through the third shift valve 350 in the same manner as in firstrange. As it does, it may flow through the second shift valve 348 (e.g.,between the first valve portion 1904 and second valve portion 1906) tothe second trim valve 314. With the second trim valve 314 in its strokedposition, the hydraulic fluid may be trimmed to a desired clutchpressure and redirected back to the second shift valve 348. As the fluidflows back to the second shift valve 348, it may flow between the fourthvalve portion 1910 and the fifth valve portion 1912 as it fills andapplies C5. As the hydraulic fluid fills and applies C5, it flows backthrough the second shift valve 348, and in particular on an underside ofthe sixth valve portion 1918, to keep the second shift valve de-strokedbefore it flows to an underside of the boost valve 354 to keep the boostvalve 354 de-stroked. The operation of the boost valve 354 is describedfurther below. The hydraulic fluid acting on the underside of the sixthvalve portion 1918 of the second shift valve 348 may function as aninterlock 1918.

To fill C1, the first shift valve 346 is in its stroked position similarto that in first range. Hydraulic fluid from the source 302 is thereforeable to flow into the first shift valve 346 (e.g., between the secondvalve portion 1806 and the third valve portion 1808) and through thesecond shift valve 348 (e.g., between the second valve portion 1906 andthird valve portion 1908) as the fluid is fed to the first trim valve310. With the first trim valve 310 stroked by the first pressure controlsolenoid 308, hydraulic fluid is able to fill and apply C1. As fluidapplies C1, hydraulic fluid is fed back to the first shift valve 346. Asit does, it may flow between fifth valve portion 1812 and the sixthvalve portion 1814 and form an interlock 1820 to maintain the firstshift valve 346 in its stroked position.

In the event of a power loss to the system, the normally low solenoids(i.e., solenoids 320 and 324) are de-energized and output zero pressure,and the normally high solenoids (i.e., solenoids 308, 312, and 316) arede-energized but still output full pressure. As a result, main pressureis still fed to the third trim valve 318, and with it being moved to itsstroked position by the third pressure control solenoid 316, hydraulicfluid is able to fill and apply C3.

During a power off event, both the first and second shift solenoids 330,332 are de-energized, and therefore the third shift valve 350 is movedto its de-stroked position. In effect, main pressure is now blocked bythe third shift valve 350 as shown in FIG. 16 and fluid is unable toflow to the second shift valve 348 and second trim valve 314. As aresult, C5 is exhausted through any of its aforementioned exhaust paths.C1 remains applied as hydraulic fluid flows from the source 302 throughthe first and second shift valves to the first trim valve 310. Thus, inthe power off event, C1 and C3 are applied to achieve fifth range. C2,C4, C5, and C6 are unapplied in this event.

As described above, the third shift valve 350 functions to blockhydraulic fluid from feeding the second trim valve 314, and thereforeneither C2 nor C5 is able to apply. Although main pressure may be fed tothe fourth and fifth trim valves, their corresponding normally lowsolenoids are de-energized and thus output zero pressure. As a result,the fourth trim valve 322 blocks fluid from filling C4 and the fifthtrim valve 326 blocks fluid from filling C6.

Referring to FIG. 8, the control system 300 may operably control thetransmission in a third forward range, or simply third range. In thirdrange, C1 and C6 are applied. Main pressure is supplied by the pressuresource 302 to the same flow paths in the system 300 as described above.The controller may energize the first pressure control solenoid 308 andthe fifth pressure control solenoid 324. As such, the first pressurecontrol solenoid 308 outputs pressure to move the first trim valve 310to its stroked position. Likewise, the fifth pressure control solenoid324 outputs pressure to move the fifth trim valve 326 to its strokedposition. The second pressure control solenoid 312, the third pressurecontrol solenoid 316, and the fourth pressure control solenoid 320 arede-energized, and thus their corresponding trim valves are disposed intheir de-stroked positions.

Main pressure is blocked by the third trim valve 318 and the fourth trimvalve 322, and pressure therefore is unable to fill and apply C3 and C4,respectively. The first and second shift solenoids 330, 332 are alsode-energized in third range, and thus the third shift valve 350 isde-stroked. With the third shift valve 350 being de-stroked, mainpressure is unable to flow to the second trim system and C2 and C5 aretherefore disengaged.

Main pressure does flow into the first shift valve 346 and the secondshift valve 348. As a result, with the first trim valve stroked,hydraulic fluid is able to flow through the first and second trim valvesand feed C1. If the transmission is upshifting from second range tothird range, C1 is already filled and applied. Hydraulic fluid from C1backfills to the first shift valve 346 and acts against a differentialarea on the first shift valve 346 to form an interlock and keep thevalve stroked.

Hydraulic fluid may also be fed from the first shift valve 346 to thefifth trim valve 326. With the fifth trim valve 326 moved to its strokedposition, fluid is able to fill and apply C6. Thus, C1 and C6 areapplied in third range.

In the event of a power loss to the controller, the control system 300is configured to control the transmission to fifth range with C1 and C3applied. In doing so, electrical current is no longer sent by thecontroller to any of the solenoids. Therefore, the normally low pressurecontrol solenoids and the first and second shift valves are de-energizedand output zero pressure. C6 is therefore exhausted when the fifth trimvalve 326 is de-stroked. C4 likewise remains unfilled with the fourthtrim valve 322 blocking main pressure. Since the second shift solenoid332 is de-energized, the third shift valve 350 is disposed in itsde-stroked position thereby blocking hydraulic fluid from flowing to thesecond trim valve 314. Even though the second pressure control solenoid312 outputs full pressure in the power off event, hydraulic fluid isblocked by the third shift valve 350 and neither C2 nor C5 can beapplied.

In third range, C1 is applied and hydraulic fluid feeding C1 furtherfeeds back to the first shift valve 346 and holds it in the strokedposition based on the interlock formed there. The first trim valve 310remains stroked since the first pressure control solenoid 308 outputsfull pressure, and C1 therefore remains applied. In addition, the thirdpressure control solenoid 316 outputs full pressure in the power offstate thereby moving the third trim valve 318 to its stroked position.Since main pressure is fed directly to the third trim system, hydraulicfluid is able to fill and apply C3. As a result, C1 and C3 are appliedin the power off state and the control system 300 defaults to fifthrange.

Referring to FIG. 9, the control system 300 is shown in an embodiment ofcontrolling the transmission in a fourth forward range or fourth range.In fourth range, C1 and C4 are applied. To do so, the controller mayenergize the first pressure control solenoid 308 and the fourth pressurecontrol solenoid 320. The first pressure control solenoid 308 outputspressure to move the first trim valve 310 to its stroked position, andthe fourth pressure control solenoid 320 outputs pressure to move thefourth trim valve 322 to its stroked position. The other pressurecontrol solenoids and the two shift solenoids are de-energized. Thus, C3and C6 are unapplied since the third trim valve 318 and the fifth trimvalve 326 are de-stroked and block fluid from filling either clutch.Moreover, with the second shift solenoid 332 de-energized, the thirdshift valve 350 is de-stroked which blocks main pressure from feedingthe second trim system. As a result, neither C2 nor C5 is able to beapplied in fourth range.

Main pressure is provided by the pressure source 302 and directly feedsthe fourth trim system, as shown in FIG. 9. With the fourth trim valve322 in its stroked position, hydraulic fluid is able to fill and applyC4. Moreover, although the first shift solenoid 330 is de-energized, C1is applied via hydraulic fluid flowing through the first shift valve andsecond shift valve to the first trim system. With C1 filled, hydraulicfluid flows back to the first shift valve 346 and the clutch pressureacting against a differential area (e.g., between valve portions 1812and 1814) on the first shift valve 346 to form the interlock 1820 andmaintain the shift valve in its stroked position. Thus, C1 and C4 areapplied in fourth range.

In the event of a power loss to the controller, C4 is exhausted when thecontroller is unable to send current to energize the fourth pressurecontrol solenoid 320. Since the fourth pressure control solenoid 320 maybe a normally low solenoid, when it is de-energized it outputs zeropressure to the trim valve. Thus, the fourth trim valve 322 de-strokesand blocks hydraulic fluid from filling C4. Similarly, C6 remainsunapplied due to the fifth trim valve 326 being de-stroked and blockingfluid.

Similar to the aforementioned first, second, and third ranges, the firstand second shift solenoids are de-energized causing the third shiftvalve 350 to be in its de-stroked position. As a result, hydraulic fluidis blocked by the third shift valve 350 and is unable to feed the secondtrim system. C2 and C5 are therefore unapplied in the power off state.

Further, the third pressure control solenoid 316 is energized andoutputs full pressure in the power off state. This moves the third trimvalve 318 to its stroked position, and since main pressure is feddirectly to the third trim system, fluid is able to fill and apply C3.

C1 is continuously fed with hydraulic fluid to remain applied during thepower off state. Even though the first shift valve 346 is not receivingcontrol main pressure from the first shift valve 330, pressure thatfills and applies C1 flows back and acts against the differential areaof the first shift valve 346 to form the interlock 1820 and keep thefirst shift valve 346 in its stroked position. As a result, when thecontrol system 300 is operating in fourth range and electrical power islost, the control system 300 defaults to fifth range with C1 and C3applied (see FIG. 16).

In FIG. 10, the control system 300 is shown in another embodiment inwhich it is operably controlling the transmission in a fifth forwardrange, or fifth range. As described previously in several of theembodiments above, fifth range may be obtained by applying C1 and C3.Fifth range also happens to be the default range during a power lossevent when the control system 300 is operably controlling thetransmission in first range, second range, third range, and fourthrange. Thus, fifth range may also be referred to as a low range defaultfor purposes of this disclosure. The control system 300 may operatedifferently when the transmission is in either reverse or neutral whenthere is a power loss, and this was described above in which the controlsystem 300 defaults to the C3 Neutral state. Here, in the lower forwardranges (i.e., first range through fifth range), the control system 300defaults to fifth range in the event of an electrical power loss. Itshould be noted that other default ranges may be possible, and fifthrange is only illustrated and described herein as one such embodiment.

To operably control the transmission in fifth range, the controller mayenergize the first pressure control solenoid 308 and the third pressurecontrol solenoid 316. In doing so, each solenoid actuates and moves thefirst trim valve 310 and third trim valve 318 to their respectivestroked positions. Main pressure is supplied by the pressure source 302directly to the third and fourth trim systems, as shown in FIG. 10. Withthe third trim valve 318 in its stroked position, hydraulic fluid isable to fill and apply C3. On the other hand, the fourth trim valve 322is in its de-stroked position thereby blocking fluid from filling C4.Similarly, the fifth trim valve is de-stroked thereby blocking fluidfrom filling and applying C6.

With the first and second shift solenoids de-energized in fifth range,there is no control main pressure being supplied to the head end of anyof the three shift valves. As such, the third shift valve 350 isde-stroked and blocks hydraulic fluid from being supplied to the secondtrim system. C2 and C5 are therefore unapplied since no hydraulic fluidis able to flow through the third shift valve 350.

C1 is applied in fifth range and it is done so by hydraulic fluidflowing through the first and second shift valves before feeding thefirst trim system. With the first trim valve 310 being in the strokedposition, hydraulic fluid is able to fill and apply C1. C1 pressure, asshown in FIG. 10, may flow back to the first shift valve 346 as it doesin second range, third range and fourth range. Here, the C5 pressureacts against a differential area on the first shift valve 346 (e.g., thesixth valve portion 1814) to form an interlock 1820, which hydraulicallyholds or maintains the first shift valve 346 in its stroked position.

Unlike the previously described forward ranges, when electrical power islost and the controller is unable to send current to any of thesolenoids in the control system 300, the same two torque-transmittingmechanism (i.e., C1 and C3) remain applied when the transmission isoperating in fifth range. In other words, when the transmission isoperating in fifth range and there is a loss of electrical power, thedefault is fifth range and so there is no shift to another range. In thepower loss state, C4 and C6 remain unapplied since the normally lowfourth pressure control solenoid 320 and the normally low fifth pressurecontrol solenoid 324 output zero pressure and the corresponding trimvalves remain de-stroked to block hydraulic fluid from filling C4 andC6. Moreover, the second shift solenoid 332 is de-energized therebyresulting in the third shift valve 350 being de-stroked. When the thirdshift valve 350 is de-stroked, hydraulic fluid is unable to flow to thesecond trim system and fill either C2 or C5. Thus, C2 and C5 areunapplied in the power loss state.

The normally high pressure control solenoids may output full pressure inthe power loss state. In view of this, the first pressure controlsolenoid 308 and third pressure control solenoid 316 output fullpressure causing the first trim valve 310 and the third trim valve 318to be disposed in their stroked positions. This allows hydraulic fluidto fill and apply C1 and C3 in the same manner as in the steady statefifth range described above.

In this disclosure, there may be three default ranges that the controlsystem 300 defaults to when electrical power is lost. The first defaultrange is C3 Neutral, and as described above, this is selected when thetransmission is operating in either reverse or neutral before the poweris lost. The second default range is fifth range with C1 and C3 applied,and this occurs when the transmission is operating in first range,second range, third range, fourth range, and fifth range. The thirddefault range is seventh range, and this occurs during a power lossevent when the transmission is operating in sixth range, seventh range,eighth range or ninth range. These latter forward ranges and the thirddefault range will be described below. However, it is to be understoodthat these default ranges are applicable to the illustrated embodimentsprovided herein. Other embodiments of the control system may default toother ranges. For example, there can be fewer than three default ranges,or in some instances, there may be more than four default ranges. Thus,this principles and teachings of this disclosure is not intended to belimited to any particular default range or number of default ranges.

Turning to FIG. 11, the control system 300 is able to operably controlthe transmission in a sixth forward range or sixth range. Here, thesecond shift valve 348 is actuated to its stroked position to allow C2to fill and apply. In addition, C1 is applied in sixth range. For C1,the controller may energize the first pressure control solenoid 308which moves the first trim valve 310 to its stroked position. Inaddition, the second pressure control solenoid 312 may be energizedthereby moving the second trim valve 314 to its stroked position. At thesame time, the third pressure control solenoid 316, the fourth pressurecontrol solenoid 320, and the fifth pressure control solenoid 324 arede-energized. Thus, hydraulic fluid is blocked by the third trim valve318, the fourth trim valve 322, and the fifth trim valve 326, whicheffectively prevents C3, C4, and C6 from filling and being applied.

In this embodiment, the first and second shift solenoids are energized.As shown, control main pressure is fed from the control main filter 336to the first shift solenoid 330 and the second shift solenoid 332. Inturn, control main pressure is fed to the head end of the first shiftvalve 346, the second shift valve 348, and the third shift valve 350.All three shift valves are thereby moved to their stroked positions.With the third shift valve 350 in its stroked position, main pressure isfed through the shift valve as shown in FIG. 17 and to the second shiftvalve 348. The hydraulic fluid is able to flow through the second shiftvalve 348 to the first trim system, and with the first trim valve 310 inits stroked position, the fluid is able to fill and apply C1.

In the same manner, hydraulic fluid from the pressure source 302 is ableto flow directly to the first shift valve 346. With the first shiftvalve 346 stroked, fluid is able to flow to the second shift valve 348where it flows to the second trim system. With the second trim valve 314in its stroked position, hydraulic fluid is able to flow through thesecond trim valve 314 and back to the second shift valve 348 where itfills and applies C2. C2 pressure further flows to the first shift valve346 and acts against another differential area on the first shift valve346 (e.g., between the fourth valve portion 1810 and the fifth valveportion 1812) to form another interlock 1818 on the first shift valve346. Thus, in sixth range, C1 and C2 are applied.

When hydraulic fluid flows to the second trim system and the second trimvalve 314 is in its stroked position, the hydraulic fluid is able toflow to the boost valve 354. The boost valve 354 may be used to “boost”or increase clutch pressure to allow a torque-transmitting mechanism tohandle high torque operating modes. In the illustrated embodiment ofFIG. 11, C2 is applied to cover the highest torque operating modes,whereas C5 may be designed such that it is unable to handle such torquemodes. C5 may be damaged due to compressive failure to elevatedpressures, and therefore the control system 300 may be designed toprevent the boost valve 354 from being actuated when C5 is engaged. Ineffect, the use or not of the boost valve 354 is a form of gain controlof the second trim system that is different from the aforementioned gaincontrol of the fifth trim system.

In at least one example, it is desirable to limit C5 pressure to belowmain pressure, whereas it is desirable for C2 pressure to beapproximately equivalent to main pressure in at least one forward range.In another example, C2 and C5 pressures may be less than main pressure,but when the boost valve is actuated, C2 pressure is capable of beinggreater than C5 pressure. In a further example, the boost valve isactuated (or stroked) when C2 is applied and deactuated (or de-stroked)when C5 is applied.

With a lower C5 pressure, the control system 300 is better able toprovide improved shift quality and controllability. Further, the secondpressure control solenoid 312 and second trim valve 314 may be able tofurther trim C5 pressure if necessary. Thus, C5 pressure is morecontrollable with the boost valve 354 de-stroked. As shown in FIG. 7,however, there is no solenoid for independently controlling movement ofthe boost valve 354. Thus, in the illustrated embodiment, C5 pressuremay be used as a blocking feature or mechanism to prevent the boostvalve 354 from moving to its stroked position when C5 is applied. Insecond range, for example, main pressure is fed to the second trimsystem via the second and third shift valves. Hydraulic fluid flowsthrough the second trim valve 314 and back to the second shift valve 348where it fills and applies C5. Once C5 is filled, fluid is able to flowback to the second trim system and it flows to a bottom side of theboost valve 354. C5 pressure therefore urges or forces the boost valve354 to remain in its de-stroked position, thereby limiting C5 pressure.The blocking feature or mechanism of the C5 pressure acting against theboost valve 354 is similar to an interlock, except that here ithydraulically holds or maintains the boost valve 354 from moving to itsstroked position. By contrast, an interlock as described herein ishydraulic pressure that hydraulically holds or maintains a valve in itsstroked position and prevents it from moving to its de-stroked position.

With the boost valve 354 hydraulically held from moving to its strokedposition, C5 pressure may be reduced and maintained below main pressure.In one embodiment, the second pressure control solenoid 312 may belimited from outputting any pressure above control main pressure. Thesecond trim valve 314 may have a gain associated with it so that C5pressure can be greater than control main pressure. For example, if thegain is 1.25 and control main pressure is 1000 kPa, then C5 pressure maybe 1250 kPa. The gain may be a function of the differential areas on thesecond trim valve 314.

In FIG. 11, the boost valve 354 may be active and C2 pressure may beapproximately main pressure. Here, as main pressure is fed to the secondtrim system and fluid flows through the second trim valve 314, it alsoflows to the boost valve 354. This flow to the boost valve 354 causesthe boost valve 354 to move to its stroked position. Moreover, with C5unapplied, there is no hydraulic fluid supplied to the bottom side ofthe boost valve 354. The boost valve 354 is therefore able to move toits stroked position and allow for increased C2 pressure. The same gainis available with the second trim valve 314, but with the boost valve354 now stroked, the second trim valve 314 can move even further to afully stroked position, for example, so that main pressure is fed to C2.In effect, the second trim valve 314 is able to be stroked further withthe boost valve 354 active so that main pressure is fed to C2. Bycontrast, with C5 applied, the second trim valve 314 is stroked but to amuch lesser degree because the boost valve 354 is inactive.

Tolerances in the second trim system may be provided via a limit on thesecond pressure control solenoid 312 or other tolerances within the mainand control main circuits.

Before returning to sixth range, it is further shown here that thesecond shift valve 348 may be provided to limit or prevent C2 and C5from both being applied at the same time. In effect, this providesfailure mode protection by allowing only one of these twotorque-transmitting mechanisms from being applied at a time.

In sixth range, the control system 300 operably controls thetransmission with C1 and C2 applied. In the event of a power loss, thecontroller may be unable to send current to any of the solenoids. Asshown in FIG. 17, another default range may be provided in the event ofa power loss while operating in sixth range. In this case, the firstshift solenoid 330 and the second shift solenoid 332 are bothde-energized. Thus, the third shift valve 350 moves to its de-strokedposition and blocks hydraulic fluid from flowing to C1. In effect, thethird shift valve 350 blocks fluid from reaching the first trim system,and thus C1 cannot be applied.

The normally low fourth pressure control solenoid 320 and the fifthpressure control solenoid 324 may be de-energized when electrical poweris lost, and therefore both solenoids do not output any pressure. As aresult, the fourth and fifth trim valves are in their de-strokedpositions and block main pressure from feeding either C4 or C6. Thus, asdescribed herein, when operating in sixth range and there is a loss ofelectrical power, C1, C4, C5 and C6 are unapplied. C2 and C3 aretherefore applied in a high default range corresponding with seventhrange.

C3 is applied in this default range due to main pressure being feddirectly to the third trim system as shown in FIG. 17. Moreover, thethird pressure control solenoid 316 may be a normally high solenoid andthus outputs full pressure when there is a loss of power. In doing so,the third trim valve 318 is actuated to its stroked position therebyallowing hydraulic fluid to fill and apply C3.

As described above, C2 is applied in sixth range. C2 pressure is able toform an interlock on both the first shift valve 346 and the second shiftvalve 348 in sixth range. Referring to FIGS. 18 and 19, for example, C2pressure may form an interlock 1818 on the first shift valve 346 andanother interlock 1916 on the second shift valve 348. Thus, even thoughcontrol main pressure is cut off when the first shift solenoid 330 isde-energized, C2 pressure is able to hold the first and second shiftvalves in their stroked positions due to the interlocks in the highdefault range. Since shift valve 348 is latched in the stroked position,main feed is blocked to C5.

As also shown in FIG. 17, the boost valve 354 may be fully stroked sothat C2 pressure may be approximately equal to main pressure. The secondtrim system may adjust C2 pressure as desired, but it is worth notingthat the both the second trim valve 312 and boost valve 354 are in theirstroked positions.

Referring now to FIG. 12, the control system 300 is shown operablycontrolling the transmission in a seventh forward range, i.e., seventhrange. In seventh range, C2 and C3 are applied as described above. Innormal or steady state seventh range shown in FIG. 12, the controllermay energize the second pressure control solenoid 312 and the thirdpressure control solenoid 316. In addition, the first pressure controlsolenoid 308, the fourth pressure control solenoid 320 and the fifthpressure control solenoid 324 are de-energized. The controller furtherenergizes the first shift solenoid 330 but de-energizes the second shiftsolenoid 332.

Hydraulic fluid may be fed to the control system 300 via the fluidpressure source 302, which as described above may be supplied by thehydraulic pump 204 of the transmission system 200. From the pressuresource 302, which may further be referred to as a main pressure circuitof the control system 300, hydraulic fluid may be fed directly to thefirst shift valve 346, the third shift valve 350, the third trim systemand the fourth trim system. With the third pressure control solenoid 316being energized, the third trim valve 318 may be moved to its stroked oropen position to allow hydraulic fluid to fill and apply C3.

With the first, fourth and fifth trim systems de-energized, therespective trim valves may block hydraulic fluid from filling C1, C4,and C6. With C1, however, hydraulic fluid may be blocked upstream viathe third shift valve 350 which is in its de-stroked position since thesecond shift solenoid 332 is de-energized.

With the first shift solenoid 330 energized, control main pressure maybe fed to the head of each of the first and second shift valves therebymoving both shift valves to their stroked positions. Main pressure maybe fed to the first shift valve directly from the pressure source 302.With the first shift valve 346 stroked, hydraulic fluid may flow throughthe first shift valve 346 and the second shift valve 348 to the secondtrim system. Since the second pressure control solenoid 312 isenergized, the second trim valve 314 may be in its stroked position, andtherefore hydraulic fluid is able to flow through the second trim systemback to the second shift valve 348 and fill and apply C2. In addition,hydraulic fluid flowing through the second trim valve further flows tothe boost valve 354 and strokes the boost valve 354 to its strokedposition. With C5 exhausted, there is no hydraulic pressure opposing theboost valve 354 from moving to its stroked position. As a result, C2pressure may be increased or boosted to approximately main pressure.

As also shown in FIG. 12, C2 pressure flows through both the first shiftvalve 346 and the second shift valve 348 and acts on differential areasor lands of both valves. In effect, C2 pressure acting on thesedifferential areas forms an interlock on both valves to hold them inplace. Since control pressure is still fed to the head of each of thefirst and second shift valves, the interlocks may be unnecessary inseventh range but the C2 pressure nevertheless fills and applieshydraulic pressure to the differential areas on both valves.

In the event of an electrical power loss, the control system 300 is ableto default to seventh range as well. Thus, when the transmission is inseventh range and there is an electrical power loss, the transmissiondoes not shift and instead stays in seventh range with C2 and C3applied. The normally high pressure control solenoids default to fulloutput pressure and the normally low pressure control solenoids defaultto zero output pressure. Thus, C4 and C6 are unapplied in the event of apower loss since both the fourth and fifth trim valves block hydraulicfluid. Moreover, the first and second shift solenoids are de-energizedand therefore the third shift valve 350 is in its de-stroked position.As such, the third shift valve 350 blocks hydraulic fluid from fillingC1.

The second pressure control solenoid 312 and the third pressure controlsolenoid 316 output full pressure in the event of an electrical powerloss. Since main pressure is fed directly to the third trim system,hydraulic fluid is able to fill and apply C3. Moreover, C2 pressureapplies interlocks on the first shift valve 346 and the second shiftvalve 348 as described above. Thus, even though the first shift solenoid330 is de-energized and no longer supplies control main to the head ofeither the first or second shift valves, the interlocks formed by C2pressure maintains both shift valves in their stroked positions. Sincethe C2 latch maintains shift valve 348 in a stroked position, mainpressure is block from feeding C5.

As also shown in FIG. 17, while the first shift solenoid 330 isde-energized in the event of an electrical power loss, control mainpressure may be slow to exhaust and still apply an interlock at the headof the second shift valve 348 as it flows through a fluid path via thethird shift valve 350. In effect, a high speed logic valve latch orinterlock may be applied to the second shift valve 348 in thisembodiment to maintain the second shift valve 348 in its strokedposition. The slow exhaust of control main pressure may be partly due tothe check valve 352 and a restriction in the fluid path. While operatingin seventh range, hydraulic fluid at control main pressure may be fedfrom the control main valve 334 directly to the main modulated solenoid340 and third shift valve 350. This same flow path will be describedbelow with respect to the actuation of the boost plug 328.

In any event, the hydraulic fluid at control main pressure is able toflow through the third shift valve (e.g., between the third valveportion 2008 and the fourth valve portion 2010) and through a firstparallel check valve 352 (located just above the third shift valve 350in FIG. 17) to the head of each of the first and second shift valves.The first check valve 352 may include a check ball that permits flow ina direction from the third shift valve 350 to the second shift valve348, but prevents a return flow of the hydraulic fluid from the secondshift valve 348 to the third shift valve 350. As a result, whenelectrical power is lost in seventh range (or forward ranges of sixth,eighth and ninth) and the first and second shift solenoids arede-energized, the hydraulic pressure at control main pressure at theheads of the first shift valve 346 and the second shift valve 348 isunable to flow back through the third shift valve 350 due to the firstcheck valve 352.

As also shown in FIG. 17, a second check valve 352 is shown located justabove the second shift valve 348. This second check valve 352 alsoincludes a check ball that allows fluid to flow from left to right inthe drawing, but the ball seats in the valve to prevent flow from rightto left. Although not shown as well in FIG. 17, a flow restrictionexists in a parallel flow path just below the second check valve 352such that hydraulic fluid is partially restricted from flowing from thesecond shift valve 348 to the first shift valve 346 (i.e., right to leftin FIG. 17). This is shown in FIG. 17 where the hydraulic fluid to theleft of the restriction is shown as exhaust and the hydraulic fluid tothe right of the restriction is shown as control main pressure. As aresult, hydraulic fluid at control main pressure at the top or head ofthe second shift valve 348 is slow to exhaust due to the restriction andthe second check valve 352. Thus, the hydraulic pressure is high enoughsuch that a latch or interlock is formed to maintain the second shiftvalve 348 in its stroked position. C2 may exhaust in this case but thefirst and second shift valves remain in their stroked positions. Othermeans may be included in other embodiments to restrict exhaust in thecontrol system 300.

It is further noted that if C2 is allowed to exhaust, a high speed C3neutral may be achieved without any actuation or movement of the firstshift valve 346 or the second shift valve 348. Thus, while it has beendescribed herein that the default to seventh range when operating in ahigher range is available, the control system 300 is also capable ofdefaulting to a high speed neutral in the event of a failure or loss ofelectrical power. Further, the second pressure switch 358 may continueto be pressurized such that the controller is able to detect theposition of the second shift valve 348 in the event of a failure orpower loss.

In addition to the high speed neutral with only C3 applied, it is alsopossible for the control system to default to seventh range with both C2and C3 applied. For example, suppose an operator is operably controllingthe transmission in a higher forward range such as sixth, seventh,eighth or ninth ranges. If the operator shifts to neutral, butelectrical power is suddenly lost, the control system may be adapted tooperably control to either the aforementioned high speed C3 neutral, oralternatively the control system may determine that the shift to neutralwas by accident and maintain C2 applied such that the transmissiondefaults to the high speed power-off range of seventh range. If theoperator does shift to neutral, and the control system detects this tobe a desired shift, then C2 may be exhausted and the transmissioncontrol system 300 may default to C3 neutral in the event of the powerloss. Moreover, if power is not lost, the control system may still endup in either C3 or C5 neutral.

Referring to FIG. 13, the control system 300 is shown operablycontrolling the transmission in an eighth forward range, or eighthrange. In eighth range, C2 and C4 are applied and the othertorque-transmitting mechanisms are unapplied. In this range, thecontroller may energize the second pressure control solenoid 312 and thefourth pressure control solenoid 320. The first, third and fifthpressure control solenoids are de-energized. Further, the controller mayenergize the first shift solenoid 330 and de-energize the second shiftsolenoid 332.

With the third shift valve 350 de-stroked due to the second shiftsolenoid 332 being de-energized, the third shift valve 350 may blockhydraulic fluid from flowing to the first trim system. Thus, C1 isblocked from receiving fluid and is thus unapplied. Further, the thirdpressure control solenoid 316 is de-energized and therefore the thirdtrim valve 318 is in its de-stroked position. In this position, mainpressure from the pressure source 302 is blocked by the third trim valve318 such that fluid is unable to fill and apply C3. C3 therefore isunapplied in eighth range.

The first shift valve 346 is directly fluidly coupled to the pressuresource 302, and with the first shift solenoid 330 being energized, thefirst shift valve 346 is in its stroked position. Hydraulic fluid istherefore able to flow through the first shift valve 346 in several flowpaths. A first flow fluidly couples the first shift valve 346 to thefifth trim system. This same fluid path is used for filling and applyingC6 when the fifth pressure control solenoid 324 is energized. In eighthrange, however, the fifth pressure control solenoid 324 is de-energized,and the fifth trim valve 326 therefore blocks the fluid path andprevents hydraulic fluid from filling and applying C6. C6 is thereforeunapplied in eighth range.

Main pressure is able to flow through a different fluid path from thefirst shift valve 346 to the second shift valve 348. Here, the secondshift valve 348 is actuated to its stroked position with the first shiftsolenoid 330 being energized and thus the second shift valve 348 isfluidly coupled to the pressure source 302. Hydraulic fluid may flowthrough the first and second shift valves to the second trim system.With the second pressure control solenoid 312 being energized, thesecond trim valve 314 may be stroked thereby allowing fluid to flowthrough the second trim valve 314. As it flows through the second trimvalve 314, the fluid flows back to the second shift valve 348 and fillsC2. C2 is therefore applied in eighth range.

In addition to filling and applying C2, hydraulic fluid is fed to theboost valve 354 and actuates boost pressure for C2. This may increase C2pressure to approximately main pressure in some embodiments. The secondtrim system may regulate or trim C2 pressure, if necessary. Moreover,with the second shift valve 348 stroked, main pressure is blocked fromfeeding C5. Thus, C5 is unable to apply in eighth range based on theposition of the second shift valve 348.

Main pressure from the fluid source 302 is directly fed or fluidlycoupled to the fourth trim system. In eighth range, the controllerenergizes the fourth pressure control solenoid 320 which actuates thefourth trim valve 322 to its stroked position. In doing so, hydraulicfluid is able to fill and apply C4 in eighth range. Thus, C2 and C4 areapplied in eighth range.

In the event electrical power is lost while operating in eighth range,the control system 300 may be designed to default to seventh range in asimilar fashion as if operating in either sixth or seventh ranges. Here,C4 is exhausted and C3 is applied. As has been described, whenelectrical power is lost, the three normally high pressure controlsolenoids output full pressure and the two normally low pressure controlsolenoids output zero pressure. Moreover, the two shift solenoids arede-energized.

With the second shift solenoid 332 being de-energized, the third shiftvalve 350 is disposed in its de-stroked position. In its de-strokedposition, the third shift valve 350 blocks hydraulic fluid from feedingC1. Further, with both normally low pressure control solenoidsde-energized, the fourth trim valve 322 and the fifth trim valve 326 arede-stroked and therefore block hydraulic fluid from feeding C4 and C6.In other words, in eighth range the fourth pressure control solenoid 320is energized by the controller so that C4 is applied, but whenelectrical power is lost the controller no longer sends current to thefourth pressure control solenoid 320. Once this happens, the fourthpressure control solenoid 320 outputs zero pressure to the fourth trimvalve 322, thereby causing the fourth trim valve 322 to move from itsstroked position to its de-stroked position. In doing so, the fourthtrim valve 322 blocks hydraulic fluid from filling C4, and C4 pressureis therefore able to exhaust.

In eighth range, C3 is unapplied but when power is lost, the thirdpressure control solenoid 316 outputs full pressure to thereby move thethird trim valve 318 to its stroked position. In doing so, main pressureis fed to the third trim system such that C3 is applied. Also, C2 isapplied in eighth range and remains applied in the event of a loss ofelectrical power. The second pressure control solenoid is a normallyhigh solenoid, and thus it outputs full pressure to keep the second trimvalve 314 stroked. C2 pressure further acts on differential areas on thefirst shift valve 346 and the second shift valve 348 to hydraulicallyhold the shift valves in their stroked positions. In other words,interlocks are formed on both shift valves to remain stroked. Shiftvalve 348 therefore blocks main feed to C5. With the first and secondshift valves stroked and the first shift valve 346 being directlyfluidly coupled with the pressure source 302, hydraulic fluid is able tocontinue to flow through both shift valves and the second trim systembefore returning to the second shift valve 348 and feeding C2. Thus, C2and C3 are applied in the high default range, i.e., seventh range, asshown in FIG. 17.

Referring to FIG. 14, the control system 300 is able to operably controlthe transmission in a ninth forward range, i.e., ninth range. In ninthrange, C2 and C6 may be applied. To do so, the controller may energizethe second pressure control solenoid 312 and the fifth pressure controlsolenoid 324. The first shift solenoid 330 is energized, but the secondshift solenoid 332 is de-energized, as shown in FIG. 14. With the firstshift solenoid 330 being energized, control main pressure is fed via thesolenoid 330 to the head of both the first shift valve 346 and thesecond shift valve 348 causing both valves to be in their strokedpositions. As will also be described below, C2 pressure may exertpressure against a differential area on both valves to form interlocksand hydraulically hold both of the first and second shift valves intheir stroked positions.

With the second and fifth pressure control solenoids being energized,the second trim valve 314 and the fifth trim valve 326 are disposed intheir stroked positions. On the other hand, with the first, third andfourth pressure control solenoids being de-energized, the first trimvalve 310, the third trim valve 318, and the fourth trim valve 322 aredisposed in their de-stroked positions. Further, with the second shiftsolenoid 332 being de-energized, the third shift valve 350 is in itsde-stroked position in ninth range.

As previously described, the second shift solenoid 332 is de-energizedin seventh and eighth ranges and, as shown in FIG. 14, it is alsode-energized in ninth range. With it de-energized, the third shift valve350 is disposed in its de-stroked position thereby blocking hydraulicfluid from being able to flow and fill C1. In effect, C1 is unable toapply when the transmission is operating in a higher range (i.e.,seventh, eighth, and ninth ranges), which provides protection to thetransmission from possible damage if C1 was to come on in any of thesehigher ranges. Thus, the third shift valve 350 provides a protectivefeature to the control system 300 and the transmission.

Since the third pressure control solenoid 316 and the fourth pressurecontrol solenoid 320 are de-energized, the third trim valve 318 andfourth trim valve 322 are de-stroked and block hydraulic fluid fromfilling either C3 or C4. Thus, in ninth range, C3 and C4 are unapplied.While this is the case, it is also shown in FIGS. 3-17 that mainpressure is fed directly from the fluid source 302 to both the third andfourth trim systems. For this reason, the mechanization chart 2100 inFIG. 21 illustrates that both C3 and C4 are capable of being applied inany range (i.e., reverse, neutral, or first through ninth ranges). Ifthe controller simply energizes either the third or fourth pressurecontrol solenoid, hydraulic fluid will fill and apply C3 or C4. Thecaveat to this is if electrical power is lost, and then the normally lowfourth pressure control solenoid 320 will be de-energized and outputzero pressure. As described herein, the fourth trim valve 322 willde-stroke and block the fluid from filling C4 when electrical power islost.

In any event, the mechanization table 2100 in FIG. 21 provides a summaryof which torque-transmitting mechanisms are available in each rangedepending upon which solenoids are energized by the controller. Thetable also shows the corresponding hydraulic default range for eachgiven steady state range in the event of a power loss. Another featureof the mechanization table 2100 is the position of each shift valve. Inthis table, a zero (0) indicates the shift valve is de-stroked, whereasa one (1) indicates the shift valve is in its stroked position. In ninthrange, for example, the first and second shift valves are shown as beingstroked (1) and the third shift valve 350 is shown being de-stroked (0).This is further supported by the embodiment of FIG. 14.

Returning to FIG. 14, the first shift valve 346 is in its strokedposition. As such, hydraulic fluid may be supplied from the source 302directly to the first shift valve 346. From the first shift valve 346,the fluid may flow to the fifth trim system. As described above, thefifth trim valve 326 is stroked to allow fluid to fill and apply C6.Although not shown as such in FIG. 14, the valve gain of the fifth trimvalve 326 is controllable such that control main pressure may be fed tothe boost plug 328. The control main pressure may flow through thechannel 344 defined in the boost plug 328 and exert a force against thehead end of the fifth trim valve 326. In doing so, the boost plug 328 isnot moved with the fifth trim valve 326 to the stroked position, therebychanging the gain across the trim system. This is in contrast to firstand third range when C6 is applied. In those ranges, control mainpressure is not fed directly to the boost plug 328, and in those lowerranges the boost plug 328 is moved in conjunction with the fifth trimvalve 326 to the stroked position.

FIG. 14 generally shows the control main pressure flowing to the boostplug 328. This control main pressure first exits the control main valve334 and control main filter 336, which is described above. The hydraulicfluid at control main pressure flows from the filter 336 and directlyfeeds into each pressure control solenoid and each shift solenoid. Inninth range, the first shift solenoid 330 is energized and outputshydraulic fluid at control main pressure to the first and second shiftvalves. Control main pressure is also fed to the main modulated solenoid340. Further, hydraulic fluid at control main pressure may also feedthrough the third valve portion 2008 and the fourth valve portion 2010of the third shift valve 350 where it flows through the check valve 352and to the head of the second shift valve 348 (i.e., on a top side ofthe first valve portion 1904). The same fluid that flows to the mainmodulated solenoid 340 and third shift valve 350 also feeds through thesecond shift valve 348 and pressurizes the second pressure switch 358.As it does so, the fluid at control main pressure is further directed tothe fifth trim system where it feeds into an opening of the boost plug328. Here, the fluid flows through the channel 344 and causes the boostplug 328 to separate from the fifth trim valve 326.

In addition to C6 being applied, C2 is also applied in a similar manneras it is in seventh and eighth ranges. Hydraulic fluid at main pressureis fed from the source 302 directly to the first shift valve 346. Withthe first shift valve 346 stroked, the fluid is able to flow to thesecond shift valve 348. With the second shift valve 348 stroked open,the hydraulic fluid is able to flow to the second trim system andthrough the second trim valve 314 (which is in its stroked position viathe second pressure control solenoid 312). As the fluid flows throughthe second trim system, it is fed back to the second shift valve 348where it fills and applies C2. C2 pressure may act on differential areasof the first shift valve 346 and the second shift valve 348 to form ahydraulic interlock on both valves. Thus, if power is lost in ninthrange and control main pressure is lost at the heads of both shiftvalves, C2 pressure is able to hydraulically hold the first shift valve346 and the second shift valve 348 in their stroked positions.

In the event of an electrical power loss while operating in ninth range,the control system 300 may be configured to default to seventh range asshown in FIG. 17. Here, the controller is unable to supply current toany of the solenoids and therefore both of the first and second shiftsolenoids are de-energized. The normally low pressure control solenoids,i.e., solenoids 320 and 324, default to outputting zero pressure andthus C6 is exhausted once the fifth trim valve 326 moves to itsde-stroked position. C4 remains exhausted as the fourth trim valve 322is in its de-stroked position.

The normally high pressure control solenoids output full pressure tomove their respective trim valves to their stroked positions. In otherwords, the first trim valve 310, the second trim valve 314, and thethird trim valve 318 are disposed in their stroked positions. C1,however, is unable to apply because hydraulic fluid is blocked upstreamby the de-stroked third shift valve 350. The latched shift valve 348also prevents fluid from flowing to the C5 clutch as well.

As shown in FIG. 17, hydraulic fluid at main pressure flows directlyfrom the pressure source 302 to the third trim system. With the thirdtrim valve 318 in its stroked and open position, fluid is able to filland apply C3. The third trim valve 318 is able to trim or reduce thehydraulic fluid from main pressure to C3 pressure to meet the needs ofthe control system 300. Thus, as described above, C2 and C3 are appliedwhen electrical power is lost when the system is previously operating inninth range. With C2 and C3 applied, the control system 300 thereforedefaults to seventh range.

A further embodiment of the present disclosure is illustrated in FIG.22. Here, one embodiment of a shift availability table 2200 isillustrated for a multispeed transmission having at least nine forwardranges, neutral, and at least one reverse. This table illustrates howmany torque-transmitting mechanisms are released or engaged betweensuccessive ranges. In first range, for example, C5 and C6 may be engaged(as shown above in the table). If an upshift to second range is desired,the table 2200 illustrates only one (1) torque-transmitting mechanismchanges between first and second ranges. As described above, C1 and C5are applied in second range. Thus, C5 is a common torque-transmittingmechanism and it remains applied during the upshift. Meanwhile, C6 maybe unapplied and C1 applied during the upshift. Similarly, if thecontroller wants to do a skip shift and upshift from first range tothird range, and thus “skip” second range, the controller is able to doso by only engaging one new torque-transmitting and disengaging onetorque-transmitting mechanism. As described above, C1 and C6 are appliedin third range. Thus, if doing a skip shift from first range to thirdrange, the controller may do so by controlling the control system 300 torelease C5 and apply C1. Here, C6 is a common torque-transmittingmechanism between first and third ranges. These shifts can be desirablebecause the controller does not have to transition the control system300 through neutral first before achieving the desired range.

In another example, the transmission may operate in fourth range with C1and C4 applied. If the controller wants to downshift to first range andskip second and third ranges, the shift availability table 2200indicates that two (2) new torque-transmitting mechanisms will need tobe applied. Moreover, both C1 and C4 will need to be disengaged duringthe downshift. Again, in first range, C5 and C6 are applied. To completethe downshift from fourth range to first range, the controller willoperably control the control system 300 such that C1 and C4 areexhausted while C5 and C6 are applied.

Further, and as described above, the design of the control system 300allows the de-energization of the second shift valve 332 to control thethird shift valve 350 to its de-stroked position, which in effect blocksthe main feed of fluid to the second trim system. As a result, C5 isunable to apply in third, fourth or fifth ranges. The logic state ofthis, however, does not negatively affect the skip shift capability ofthe control system 300. Moreover, in seventh, eighth and ninth ranges,the third shift valve 350 is controlled to its de-stroked position whicheffectively blocks the main feed of hydraulic fluid to the first trimsystem. Thus, C1 cannot be applied in these higher ranges and thusprovides an improved failure mode protection to the control system 300,and it is able to do so without impacting the system's skip shiftcapability.

For purposes of this disclosure, an upshift may refer to a shifttransition from a lower range to a higher range (e.g., first range tosecond range), and a downshift may refer to a shift transition from ahigher range to a lower range (e.g., second range to first range). Askip shift may include either an upshift or a downshift, but when it isachieved, the control system skips one or more intermediate ranges whencompleting the shift transition (e.g., fourth range to first range skipssecond and third ranges). In addition, a gear ratio from an input to anoutput of the transmission may be greater than 1.0 at the lower ranges,whereas the gear ratio may be less than 1.0 at the higher ranges. In oneembodiment, one of the ranges may provide a gear ratio equal to orapproximately 1.0. In any event, the gear ratio may depend upon thearchitecture of the transmission, and one skilled in the art willappreciate different gear ratios based on different multispeedtransmission architectures. Thus, the present disclosure does notprovide any specific gear ratio for any given range.

While exemplary embodiments incorporating the principles of the presentdisclosure have been disclosed hereinabove, the present disclosure isnot limited to the disclosed embodiments. Instead, this application isintended to cover any variations, uses, or adaptations of the disclosureusing its general principles. Further, this application is intended tocover such departures from the present disclosure as come within knownor customary practice in the art to which this disclosure pertains andwhich fall within the limits of the appended claims.

The invention claimed is:
 1. An electro-hydraulic control system for amultispeed transmission, comprising: a controller for operablycontrolling the transmission; a fluid source for supplying hydraulicfluid; a plurality of torque-transmitting mechanisms being operablyselected between an applied and an unapplied state to achieve aplurality of ranges including at least one reverse, a neutral, and aplurality of forward ranges, wherein in any one of the plurality offorward ranges only two of the plurality of torque-transmittingmechanisms are in the applied state; a plurality of trim systems beingin electrical communication with the controller and in fluidcommunication with the fluid source, wherein each of the plurality oftrim systems includes a pressure control solenoid and a trim valve; aplurality of shift valves each of which is disposed in fluidcommunication with the fluid source and configured to move between astroked position and a de-stroked position, the plurality of shiftvalves including at least a first shift valve, a second shift valve anda third shift valve; wherein, when operating in a first forward range ata high transmission output speed, a first torque-transmitting mechanismand a second torque-transmitting mechanism are in their applied statesand the other of the plurality of torque-transmitting mechanisms are intheir unapplied states; wherein, when a shift from the first forwardrange to neutral is made immediately followed by a loss of electricalpower in the system, a hydraulic latch is formed by hydraulic fluidagainst at least one of the first, second and third shift valves suchthat the at least one of the first, second and third shift valves ismaintained in its stroked position due to the latch.
 2. The system ofclaim 1, further comprising a check valve located between the at leastone of the first, second and third shift valves and an exhaust passageto form the latch.
 3. The system of claim 1, wherein hydraulic fluidflows from the third shift valve to the second shift valve to form thehydraulic latch and maintain the second shift valve in its strokedposition following the shift and loss of electrical power.
 4. The systemof claim 1, wherein following the shift and loss of electrical power,the system defaults to one of the plurality of forward ranges such thatthe first torque-transmitting mechanism remains in its applied state andone of the other plurality of torque-transmitting mechanisms is disposedin its applied state.
 5. The system of claim 1, further comprising apressure switch disposed in fluid communication with the at least one ofthe first, second and third shift valves and in electrical communicationwith the controller, the pressure switch configured to detect a positionof the at least one of the first, second and third shift valves.
 6. Thesystem of claim 1, wherein the first torque-transmitting mechanismremains in its applied state and the second torque-transmittingmechanism exhausts to its unapplied state during the shift to neutralsuch that only the first of the plurality of torque-transmittingmechanisms is in its applied state.
 7. The system of claim 1, whereinthe latch is formed by a flow restriction and check valve locatedbetween the at least one of the first, second and third shift valves andan exhaust passage.
 8. An electro-hydraulic control system for amultispeed transmission, comprising: a controller for operablycontrolling the transmission; a fluid source for supplying hydraulicfluid; a plurality of torque-transmitting mechanisms being operablyselected between an applied and an unapplied state to achieve aplurality of ranges including at least one reverse, a neutral, and aplurality of forward ranges, wherein in any one of the plurality offorward ranges only two of the plurality of torque-transmittingmechanisms are in the applied state; a plurality of trim systems beingin electrical communication with the controller and in fluidcommunication with the fluid source, wherein each of the plurality oftrim systems includes a pressure control solenoid and a trim valve; aplurality of shift valves each of which is disposed in fluidcommunication with the fluid source and configured to move between astroked position and a de-stroked position, the plurality of shiftvalves including at least a first shift valve, a second shift valve anda third shift valve; a first shift solenoid and a second shift solenoideach of which is disposed in electrical communication with thecontroller, only the first shift solenoid being operably controlledbetween an energized and de-energized states to control movement of thefirst and second shift valves, and the second shift solenoid beingoperably controlled between an energized and de-energized states tocontrol movement of the third shift valve; wherein: in a first forwardrange of the plurality of forward ranges, a first torque-transmittingmechanism and a second torque-transmitting mechanism are in theirapplied states; only the first shift solenoid is energized to controlmovement of the first and second shift valves to their stroked positionssuch that hydraulic fluid at a head of each of the first and secondshift valves forces both shift valves to their stroked positions;further wherein, when shifting from the first forward range to neutral,the first torque-transmitting mechanism remains in its applied state asthe only applied torque-transmitting mechanism, and the secondtorque-transmitting mechanism is exhausted.
 9. The system of claim 8,wherein, during a loss of electrical power in the system, a latch isformed by hydraulic fluid in the system against at least one of thefirst, second and third shift valves when shifting to neutral from thefirst forward range to maintain the at least one of the first, secondand third shift valves in its stroked position.
 10. The system of claim9, wherein at least one of the first and second shift valves ismaintained in its stroked position due to the latch, and the third shiftvalve is maintained in its de-stroked position.
 11. The system of claim9, wherein the first and second shift valves are maintained in theirstroked positions due to the latch.
 12. The system of claim 9, whereinthe latch is formed by a check valve located between the at least one ofthe first, second and third shift valves and an exhaust passage.
 13. Thesystem of claim 9, wherein the latch is formed by a flow restriction andcheck valve located between the at least one of the first, second andthird shift valves and an exhaust passage.
 14. The system of claim 8,further comprising a pressure switch disposed in fluid communicationwith the at least one of the first, second and third shift valves and inelectrical communication with the controller, the pressure switchconfigured to detect a position of the at least one of the first, secondand third shift valves.
 15. An electro-hydraulic control system for amultispeed transmission, comprising: a controller for operablycontrolling the transmission; a fluid source for supplying hydraulicfluid; a plurality of torque-transmitting mechanisms being operablyselected between an applied and an unapplied state to achieve aplurality of ranges including at least one reverse, a neutral, and aplurality of forward ranges, wherein in any one of the plurality offorward ranges only two of the plurality of torque-transmittingmechanisms are in the applied state; a plurality of trim systems beingin electrical communication with the controller and in fluidcommunication with the fluid source, wherein each of the plurality oftrim systems includes a pressure control solenoid and a trim valve; aplurality of shift valves each of which is disposed in fluidcommunication with the fluid source and configured to move between astroked position and a de-stroked position, the plurality of shiftvalves including at least a first shift valve, a second shift valve anda third shift valve; a first shift solenoid disposed in electricalcommunication with the controller, only the first shift solenoid beingoperably controlled between an energized and de-energized states tocontrol movement of the first and second shift valves; and a secondshift solenoid disposed in electrical communication with the controller,the second shift solenoid being operably controlled between an energizedand de-energized states to control movement of the third shift valve;wherein, movement of the first shift valve between its stroked andde-stroked positions is operably controlled by the controller to selecta desired range of the plurality of ranges.
 16. The system of claim 15,wherein: in neutral and the at least one reverse, the controlleroperably controls movement of the first shift valve to its de-strokedposition; and in each of the plurality of forward ranges, the controlleroperably controls movement of the first shift valve to its strokedposition.
 17. The system of claim 15, further comprising a plurality ofpressure switches disposed in electrical communication with thecontroller, the plurality of pressure switches comprising at least afirst pressure switch, a second pressure switch and a third pressureswitch.
 18. The system of claim 17, wherein: the first pressure switchis in fluid communication with the first shift valve to detect aposition thereof; the second pressure switch is in fluid communicationwith the second shift valve to detect a position thereof; and the thirdpressure switch is in fluid communication with the third shift valve todetect a position thereof.
 19. The system of claim 18, wherein: inneutral and the at least one reverse, the controller operably controlsmovement of the first shift valve to its de-stroked position; in each ofthe plurality of forward ranges, the controller operably controlsmovement of the first shift valve to its stroked position; the firstpressure switch is either pressurized or not pressurized based on theposition of the first shift valve; and the controller operably detectsthe position of the first shift valve based on whether the firstpressure switch is pressurized or not pressurized.
 20. The system ofclaim 17, further comprising: a fourth pressure switch disposed in fluidcommunication with a first trim system of the plurality of trim systems;and a first torque-transmitting mechanism of the plurality oftorque-transmitting mechanisms being in fluid communication with thefirst trim system; wherein, the fourth pressure switch is eitherpressurized or not pressurized based upon a position of the trim valveof the first trim system; further wherein, the position of the trimvalve and whether the first torque-transmitting mechanism is in itsapplied state or unapplied state is operably detectable by thecontroller based on if the fourth pressure switch is pressurized or not.